IMac 21,5": Hangs or shuts down

Question

Hello all!
My iMac 21,5" hangs or shuts down once in a while.
It also gets really slow, especially when saving a file in Adobe Illustrator CS6 and than switching to the finder.
I hope somebody can help me.
Many thanks.
Details:
Model Name:    iMac
Model Identifier:    iMac13,1
Processor Name:    Intel Core i5
Processor Speed:    2.7 GHz
Number of Processors:    1
Total Number of Cores:    4
L2 Cache (per Core):    256 KB
L3 Cache:    6 MB
Memory:    16 GB
Kernel Panic:
Interval Since Last Panic Report:  863847 sec
Panics Since Last Report:          1
Anonymous UUID:
Mon Sep 23 17:09:30 2013
panic(cpu 0 caller 0xffffff7f8f51ff33): NVRM[0/1:0:0]: Read Error 0x00000144: CFG 0x0fd810de 0x00100406 0xb0000000, BAR0 0x103000000 0xffffff81e0f99000 0x0e7180a2, D0, P0/4
Backtrace (CPU 0), Frame : Return Address
0xffffff81cf8fbcc0 : 0xffffff800ec1d626
0xffffff81cf8fbd30 : 0xffffff7f8f51ff33
0xffffff81cf8fbdf0 : 0xffffff7f8f5f412d
0xffffff81cf8fbe30 : 0xffffff7f8f90be2e
0xffffff81cf8fbe50 : 0xffffff7f8f526c67
0xffffff81cf8fbef0 : 0xffffff7f8f4c4651
0xffffff81cf8fbf10 : 0xffffff800f04a9c8
0xffffff81cf8fbf40 : 0xffffff7f8f173865
0xffffff81cf8fbf50 : 0xffffff7f90faaead
0xffffff81cf8fbf60 : 0xffffff7f90fb250b
0xffffff81cf8fbf80 : 0xffffff800ecb7c8f
0xffffff81cf8fbfd0 : 0xffffff800ecce338
0xffffff81e08a3890 : 0xffffff7f8f6bbfba
0xffffff81e08a38b0 : 0xffffff7f8f6ccceb
0xffffff81e08a3a40 : 0xffffff7f8f4c0970
0xffffff81e08a3ac0 : 0xffffff7f8f4ac57b
0xffffff81e08a3b30 : 0xffffff7f8f4ac9dd
0xffffff81e08a3b70 : 0xffffff7f8f472a6d
0xffffff81e08a3bc0 : 0xffffff800f0681f3
0xffffff81e08a3c20 : 0xffffff800f065e2f
0xffffff81e08a3d70 : 0xffffff800ec98c01
0xffffff81e08a3e80 : 0xffffff800ec20b3d
0xffffff81e08a3eb0 : 0xffffff800ec10448
0xffffff81e08a3f00 : 0xffffff800ec1961b
0xffffff81e08a3f70 : 0xffffff800eca6536
0xffffff81e08a3fb0 : 0xffffff800ecce9e3
      Kernel Extensions in backtrace:
         com.apple.iokit.IOPCIFamily(2.7.3)[1D668879-BEF8-3C58-ABFE-FAC6B3E9A292]@0xffff ff7f8f172000->0xffffff7f8f196fff
         com.apple.driver.AppleACPIPlatform(1.7)[D49DC2E0-97DF-32E6-A8ED-7A12EF1AA51B]@0 xffffff7f90fa4000->0xffffff7f90ffbfff
            dependency: com.apple.iokit.IOACPIFamily(1.4)[A35915E8-C1B0-3C0F-81DF-5515BC9002FC]@0xfffff f7f8fe1e000
            dependency: com.apple.iokit.IOPCIFamily(2.7.3)[1D668879-BEF8-3C58-ABFE-FAC6B3E9A292]@0xffff ff7f8f172000
         com.apple.iokit.IOGraphicsFamily(2.3.7)[990D1A42-DF16-3AB9-ABC1-6A88AC142244]@0 xffffff7f8f467000->0xffffff7f8f49efff
            dependency: com.apple.iokit.IOPCIFamily(2.7.3)[1D668879-BEF8-3C58-ABFE-FAC6B3E9A292]@0xffff ff7f8f172000
         com.apple.iokit.IONDRVSupport(2.3.7)[6C8CFC18-75F0-3DEF-86C7-CEB2C1FD6BB1]@0xff ffff7f8f4aa000->0xffffff7f8f4bbfff
            dependency: com.apple.iokit.IOGraphicsFamily(2.3.7)[990D1A42-DF16-3AB9-ABC1-6A88AC142244]@0 xffffff7f8f467000
            dependency: com.apple.iokit.IOPCIFamily(2.7.3)[1D668879-BEF8-3C58-ABFE-FAC6B3E9A292]@0xffff ff7f8f172000
         com.apple.NVDAResman(8.1.2)[96AE69DE-8A37-39D0-B2D3-D8446A6AA670]@0xffffff7f8f4 be000->0xffffff7f8f763fff
            dependency: com.apple.iokit.IOPCIFamily(2.7.3)[1D668879-BEF8-3C58-ABFE-FAC6B3E9A292]@0xffff ff7f8f172000
            dependency: com.apple.iokit.IONDRVSupport(2.3.7)[6C8CFC18-75F0-3DEF-86C7-CEB2C1FD6BB1]@0xff ffff7f8f4aa000
            dependency: com.apple.iokit.IOGraphicsFamily(2.3.7)[990D1A42-DF16-3AB9-ABC1-6A88AC142244]@0 xffffff7f8f467000
         com.apple.nvidia.gk100hal(8.1.2)[8007AA34-6789-37E9-B069-A414AA26C6B6]@0xffffff 7f8f76f000->0xffffff7f8faa0fff
            dependency: com.apple.NVDAResman(8.1.2)[96AE69DE-8A37-39D0-B2D3-D8446A6AA670]@0xffffff7f8f4 be000
            dependency: com.apple.iokit.IOPCIFamily(2.7.3)[1D668879-BEF8-3C58-ABFE-FAC6B3E9A292]@0xffff ff7f8f172000
BSD process name corresponding to current thread: WindowServer
Mac OS version:
12E55
Kernel version:
Darwin Kernel Version 12.4.0: Wed May  1 17:57:12 PDT 2013; root:xnu-2050.24.15~1/RELEASE_X86_64
Kernel UUID: 896CB1E3-AB79-3DF1-B595-549DFFDF3D36
Kernel slide:     0x000000000ea00000
Kernel text base: 0xffffff800ec00000
System model name: iMac13,1 (Mac-00BE6ED71E35EB86)
System uptime in nanoseconds: 30955729284596
last loaded kext at 3449783312757: com.apple.driver.AppleUSBCDC          4.1.23 (addr 0xffffff7f910ab000, size 16384)
last unloaded kext at 3509845520518: com.apple.driver.AppleUSBCDC          4.1.23 (addr 0xffffff7f910ab000, size 12288)
loaded kexts:
com.apple.filesystems.afpfs          10.0
com.apple.nke.asp_tcp          7.1.0
com.apple.filesystems.smbfs          1.8.4
com.apple.driver.AudioAUUC          1.60
com.apple.driver.AppleBluetoothMultitouch          75.19
com.apple.driver.AppleHWSensor          1.9.5d0
com.apple.driver.AGPM          100.12.87
com.apple.driver.X86PlatformShim          1.0.0
com.apple.driver.ApplePlatformEnabler          2.0.6d1
com.apple.driver.AppleMikeyHIDDriver          122
com.apple.filesystems.autofs          3.0
com.apple.driver.AppleHDA          2.3.7fc4
com.apple.GeForce          8.1.2
com.apple.driver.AppleUpstreamUserClient          3.5.10
com.apple.iokit.BroadcomBluetoothHCIControllerUSBTransport          4.1.4f2
com.apple.iokit.IOUserEthernet          1.0.0d1
com.apple.iokit.IOBluetoothSerialManager          4.1.4f2
com.apple.driver.AppleSMCLMU          2.0.3d0
com.apple.driver.AppleLPC          1.6.0
com.apple.driver.AppleMikeyDriver          2.3.7fc4
com.apple.Dont_Steal_Mac_OS_X          7.0.0
com.apple.driver.ApplePolicyControl          3.4.5
com.apple.driver.AppleIntelHD4000Graphics          8.1.2
com.apple.driver.AppleMCCSControl          1.1.11
com.apple.driver.AppleIntelFramebufferCapri          8.1.2
com.apple.AppleFSCompression.AppleFSCompressionTypeDataless          1.0.0d1
com.apple.AppleFSCompression.AppleFSCompressionTypeZlib          1.0.0d1
com.apple.BootCache          34
com.apple.driver.XsanFilter          404
com.apple.driver.AppleSDXC          1.4.2
com.apple.iokit.IOAHCIBlockStorage          2.3.1
com.apple.iokit.AppleBCM5701Ethernet          3.6.1b4
com.apple.driver.AppleUSBHub          5.5.5
com.apple.driver.AirPort.Brcm4331          615.20.17
com.apple.driver.AppleAHCIPort          2.5.2
com.apple.driver.AppleUSBEHCI          5.5.0
com.apple.driver.AppleUSBXHCI          5.6.0
com.apple.driver.AppleEFINVRAM          1.7
com.apple.driver.AppleACPIButtons          1.7
com.apple.driver.AppleRTC          1.5
com.apple.driver.AppleHPET          1.8
com.apple.driver.AppleSMBIOS          1.9
com.apple.driver.AppleACPIEC          1.7
com.apple.driver.AppleAPIC          1.6
com.apple.driver.AppleIntelCPUPowerManagementClient          196.0.0
com.apple.nke.applicationfirewall          4.0.39
com.apple.security.quarantine          2.1
com.apple.driver.AppleIntelCPUPowerManagement          196.0.0
com.apple.security.SecureRemotePassword          1.0
com.apple.driver.IOBluetoothHIDDriver          4.1.4f2
com.apple.driver.AppleMultitouchDriver          235.29
com.apple.kext.triggers          1.0
com.apple.driver.DspFuncLib          2.3.7fc4
com.apple.iokit.IOAudioFamily          1.8.9fc11
com.apple.kext.OSvKernDSPLib          1.6
com.apple.nvidia.gk100hal          8.1.2
com.apple.NVDAResman          8.1.2
com.apple.iokit.AppleBluetoothHCIControllerUSBTransport          4.1.4f2
com.apple.iokit.IOSurface          86.0.4
com.apple.iokit.IOSerialFamily          10.0.6
com.apple.iokit.IOBluetoothFamily          4.1.4f2
com.apple.driver.AppleHDAController          2.3.7fc4
com.apple.iokit.IOHDAFamily          2.3.7fc4
com.apple.driver.AppleThunderboltEDMSink          1.1.8
com.apple.driver.AppleThunderboltEDMSource          1.1.8
com.apple.driver.X86PlatformPlugin          1.0.0
com.apple.driver.AppleSMC          3.1.4d2
com.apple.driver.IOPlatformPluginFamily          5.3.0d51
com.apple.driver.AppleSMBusPCI          1.0.11d0
com.apple.iokit.IOAcceleratorFamily          74.5.1
com.apple.driver.AppleGraphicsControl          3.4.5
com.apple.iokit.IONDRVSupport          2.3.7
com.apple.driver.AppleSMBusController          1.0.11d0
com.apple.iokit.IOGraphicsFamily          2.3.7
com.apple.iokit.IOSCSIArchitectureModelFamily          3.5.5
com.apple.driver.AppleUSBHIDKeyboard          170.2
com.apple.driver.AppleHIDKeyboard          170.2
com.apple.iokit.IOUSBHIDDriver          5.2.5
com.apple.driver.AppleThunderboltDPOutAdapter          1.8.9
com.apple.driver.AppleThunderboltDPInAdapter          1.8.9
com.apple.driver.AppleThunderboltDPAdapterFamily          1.8.9
com.apple.driver.AppleThunderboltPCIDownAdapter          1.2.6
com.apple.driver.AppleUSBMergeNub          5.5.5
com.apple.driver.AppleUSBComposite          5.2.5
com.apple.iokit.IOEthernetAVBController          1.0.2b1
com.apple.driver.AppleThunderboltNHI          1.7.8
com.apple.iokit.IOThunderboltFamily          2.4.0
com.apple.iokit.IO80211Family          530.4
com.apple.iokit.IONetworkingFamily          3.0
com.apple.iokit.IOUSBUserClient          5.5.5
com.apple.iokit.IOAHCIFamily          2.3.1
com.apple.iokit.IOUSBFamily          5.6.0
com.apple.driver.AppleEFIRuntime          1.7
com.apple.iokit.IOHIDFamily          1.8.1
com.apple.iokit.IOSMBusFamily          1.1
com.apple.security.sandbox          220.3
com.apple.kext.AppleMatch          1.0.0d1
com.apple.security.TMSafetyNet          7
com.apple.driver.DiskImages          345
com.apple.iokit.IOStorageFamily          1.8
com.apple.driver.AppleKeyStore          28.21
com.apple.driver.AppleACPIPlatform          1.7
com.apple.iokit.IOPCIFamily          2.7.3
com.apple.iokit.IOACPIFamily          1.4
com.apple.kec.corecrypto          1.0
System Profile:
Model: iMac13,1, BootROM IM131.010A.B05, 4 processors, Intel Core i5, 2.7 GHz, 16 GB, SMC 2.9f8
Graphics: NVIDIA GeForce GT 640M, NVIDIA GeForce GT 640M, PCIe, 512 MB
Memory Module: BANK 0/DIMM0, 8 GB, DDR3, 1600 MHz, 0x02FE, 0x45424A3831554738424255352D474E2D4620
Memory Module: BANK 1/DIMM0, 8 GB, DDR3, 1600 MHz, 0x02FE, 0x45424A3831554738424255352D474E2D4620
AirPort: spairport_wireless_card_type_airport_extreme (0x14E4, 0xF4), Broadcom BCM43xx 1.0 (5.106.98.100.17)
Bluetooth: Version 4.1.4f2 12041, 2 service, 18 devices, 1 incoming serial ports
Network Service: Ethernet, Ethernet, en0
Serial ATA Device: APPLE HDD ST1000LM024, 1 TB
USB Device: hub_device, 0x8087  (Intel Corporation), 0x0024, 0x1a100000 / 2
USB Device: Keyboard Hub, apple_vendor_id, 0x1006, 0x1a120000 / 4
USB Device: CTH-470, 0x056a  (WACOM Co., Ltd.), 0x00de, 0x1a123000 / 6
USB Device: Apple Keyboard, apple_vendor_id, 0x0221, 0x1a122000 / 5
USB Device: FaceTime HD Camera (Built-in), apple_vendor_id, 0x8511, 0x1a110000 / 3
USB Device: hub_device, 0x8087  (Intel Corporation), 0x0024, 0x1d100000 / 2
USB Device: hub_device, 0x0424  (SMSC), 0x2412, 0x1d180000 / 3
USB Device: BRCM20702 Hub, 0x0a5c  (Broadcom Corp.), 0x4500, 0x1d181000 / 4
USB Device: Bluetooth USB Host Controller, apple_vendor_id, 0x828b, 0x1d181300 / 5

Answer 1

That panic was not caused by third-party software. If the problem is recurrent, the possibilities are:
A stale or corrupt kernel cache
A damaged OS X installation
A fault in a peripheral device, if any
Corrupt non-volatile memory (NVRAM)
An internal hardware fault (including incompatible memory)
An obscure bug in OS X
You may already have ruled out some of these.
Rule out #1 by booting in safe mode and then rebooting as usual. Note: If FileVault is enabled on some models, or if a firmware password is set, or if the boot volume is a software RAID, you can’t do this. Post for further instructions.
You can rule out #2 and #3 by reinstalling the OS and testing with non-essential peripherals disconnected and aftermarket expansion cards removed, if applicable. Sometimes a clean reinstallation (after erasing the startup volume) may solve a problem that isn't solved by reinstalling in place, without erasing.
Corrupt NVRAM, which rarely causes panics, can be ruled out by resetting it.
If your model has user-replaceable memory, and you've upgraded the memory modules, reinstall the original memory and see whether there's any improvement. Be careful not to touch the gold contacts. Clean them with a mild solvent such as rubbing alcohol. Aftermarket memory must exactly match the technical specifications for your model.
The Apple Hardware Test or Apple Diagnostics, though generally unreliable, will sometimes detect a fault. A negative test can't be depended on. Run the extended version of the test.
In the category of obscure bugs, reports suggest that FileVault may trigger kernel traps under some unknown conditions. Most, though not all, of these reports seem to involve booting from an aftermarket SSD. If those conditions apply to you, try deactivating FileVault.
Connecting more than one display is another reported trigger for OS X bugs.
If your system is not fully up to date, running Software Update might get you a bug fix.
In rare cases, a malformed network packet from a defective router or other network device can cause panics. Such packets could also be sent deliberately by a skillful attacker. This possibility is something to consider if you run a public server that might be the target of such an attack.
If none of the above applies, make a "Genius" appointment at an Apple Store to have the machine tested. You may have to leave it there for several days. There isn't much point in doing this unless you can reproduce the panic, or if you can't, it happens often enough that it's likely to be repeated at the store. Otherwise you may be told that nothing is wrong.
Print the first page of the panic report and bring it with you.
Back up all data on the internal drive(s) before you hand over your computer to anyone. If privacy is a concern, erase the data partition(s) with the option to write zeros* (do this only if you know how to restore, and you have at least  two independent backups.) Don’t erase the recovery partition, if present.
Keeping your confidential data secure during hardware repair
*An SSD doesn't need to be zeroed.