every time my computer is idle or im playin a game like sims 2 or fallout 3 it locks up or reboots. ive done virus scans and mailware scan and there was nothing. ive done hardware test and all is ok. what could be wrong

Could be that your pc is over heating, also turn of the the restart on error heres how 1. Click Start Right-click My Computer, and then click Properties. 2. Click the Advanced tab. 3. Under Startup and Recovery, click Settings to open the Startup and Recovery dialog box. 4. Clear the Automatically restart check box, and click OK the necessary number of times. 5. Restart your computer for the settings to take effect. This will through an error when something goes wrong which should help identify where the problem is. I would suggest that you also check inside you machine to see if your heatsink and fan assembly are 1. seated properly 2. Clean from dust 3. Fan is spinning 4. Check the temps of your machine either through BIOS or something like Speedfan or Everest home edition lets us know what you find. Bunty

Its not overheating ive checked that

Ok how did you check that? What temps are showing?

I used speed fan and it showed the cpu and both hard drives and they were all ok. i even but a box fan blowin into it with theside off