Why do my mac stops while i'm working?

Question

When i'm working or simply playing games my Imac G5 go on standby by it's own, first the fan makes a noise like an helicopter and than the comp goes on stand by, sometimes it stop too.
When I move the mouse the comp resurrect making loud noise, but after a while goes down again, someone knows why? What I can try?
Thank you in advance
Monica

Answer 1

Hi--
It sounds to me like it's overheating. Make sure it's in a well ventilated area. There are a few things to look out for:
1. Make sure there's nothing blocking the vents at the bottom of the screen. The iMac pulls in air at the bottom. This could be pet hair, or dust, or even papers on the desk below the screen.
2. Make sure the vents in the back are not blocked. The air from the bottom is pulled up through the case and exits out the back behind the screen.
3. Make sure the hot air that vents out the back isn't being forced back down into the case at the bottom. For example, if you have your iMac in a tight cabinet with a closed back, you might have problems with it overheating.
4. If you've opened the back, or had any service done, make sure the back is on tightly. If the back isn't tightly (which happened to me), the fans inside the iMac can't cool the electronics efficiently.
One way to be sure if it is overheating is to open up the Console application in your Utilities folder and look at the Console Log. If you see entries like this, it's overheating:
May 28 11:04:15 localhost kernel: Thermal Manager: max temperature exceeded for 30 seconds, forcing system sleep
May 28 11:04:15 localhost kernel: SMUNeo2PlatformPlugin core dump:
May 28 11:04:15 localhost kernel: IOHWControls:
May 28 11:04:15 localhost kernel: [0] "System" Type:"fan-rpm" Id:0 TGT:1240 CUR:1232
May 28 11:04:15 localhost kernel: [1] "Hard Drive" Type:"fan-rpm" Id:2 TGT:1800 CUR:1794
May 28 11:04:15 localhost kernel: [2] "CPU" Type:"fan-rpm" Id:1 TGT:4400 CUR:4378
May 28 11:04:15 localhost kernel: [3] "sysclk slew" Type:"slew" Id:256 TGT:1 CUR:1
May 28 11:04:15 localhost kernel: IOHWSensors:
May 28 11:04:15 localhost kernel: [0] "CPU Power" Type:"power" Id:5 CUR:11.36356 W
May 28 11:04:15 localhost kernel: [1] "CPU T-Diode" Type:"temp" Id:0 CUR:85.16394 C
May 28 11:04:15 localhost kernel: [2] "CPU Current" Type:"current" Id:1 CUR:1.12416 A
May 28 11:04:15 localhost kernel: [3] "CPU Voltage" Type:"voltage" Id:2 CUR:12.1728 V
May 28 11:04:15 localhost kernel: [4] "Hard drive" Type:"temperature" Id:4 CUR:48.0 C
May 28 11:04:15 localhost kernel: IOHWCtrlLoops:
May 28 11:04:15 localhost kernel: [0] "Clock Slew" Id:0 MetaState:1 "Force Reduced Speed"
May 28 11:04:15 localhost kernel: [1] "PowerMac8,1 B System Fans" Id:1 MetaState:0 "Normal"
May 28 11:04:15 localhost kernel: [2] "CPU Fan" Id:2 MetaState:0
charlie