Yosemite only boots in single user mode?!

Question

Hello everyone,
for a few weeks now I've had issues with unresponsive wakes and whatnot but now it seems my machine has detiorated within a short walk home.
First off my specs:
MBP 13" mid 2012
Core i5 2,5Ghz, Intel HD4000
2x 4gb Ram 1600MHz
Samsung 840 Evo 120Gb SSD
As I said, within 20 minutes of carrying the laptop around the performance deteriorated drastically. When I opened it up back home it was incredibly slow and unresponsive. Opening Applications or even just folders takes about 30-60 seconds. Same applies for using the brightness controls for screen and keyboard, or the volume buttons. After some 15 minutes the System will completely stop to react to startup attempts of applications.
I tried the following troubleshoots while searching the forums as I understand this is a common problem in Yosemite:
- boot in safe mode ( worked once, but with the same problems of unresponsiveness, after a second try booting hangs at the usual 50%)
- reset SMC
- reset NVRAM ( PRAM?)
- try to repair the disk via disk recovery ( cmd + r)( repair failed and Volume vanished from the list - after that only internet recovery was available) ( also of note: today I brought my SSD up to its limit by installing unreal engine 4. I deleted it expecting to see an improvement, which I didn't get. Still, after deinstalling it the Volume showed a 99% utilization in disk recovery)
- starting single user mode and this is interesting. First it shows the following without any input:
Warning: Couldn't block sleep during cache update
Warning: Proceeding without DlskArb
rebuilding .../Caches/com.apple.kext.caches/Startup/kernelcache
pci pause: SDXC
IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
IOBluetoothHostControllerUARTTransport.kext has no Info.plist file.
kext file:///System/Library/Extensions/JMlcromATA.kext/ is in hash exception list, allowing to load
Child process / user/sbin/kextcache[6] exited due to signal 11.
Error 107 rebuilding /System/Library/Caches/com.apple.kext.cashes/Startup/kernelcache
then it proceeds to boot into the same unresponsive mess as before.
- In the finder I tried to repair disk permissions and again the volume itself to no avail.
I really have no idea what to do about it at this point. I can recreate this scenario and reliably boot this way but the system is painfully slow and impossible to work with. Sorry to bring up this topic again since there have been so many posts on similar problems but none of the aforementioned solutions worked for me.

Answer 1

Please do the following:
Install or Reinstall OS X from Scratch
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Erase the hard drive:
  1. Select Disk Utility from the main menu and click on the Continue button.
  2. After DU loads select your startup volume (usually Macintosh HD) from the
      left side list. Click on the Erase tab in the DU main window.
  3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on
      the Security button and set the Zero Data option to one-pass. Click on
      the Erase button and wait until the process has completed.
  4. Quit DU and return to the main menu.
Reinstall OS X: Select Reinstall OS X and click on the Install button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible
           because it is three times faster than wireless.
This should install the version of OS X that you had installed.