I would think it is unlikely to be motherboard. Have you considered overheating of something that you can`t monitor?
Can you start in `Safe Mode`?
You could also try booting from CD (XP or ATI recovery disk?) and see if the PC continues to run, if it does then try running sfc/scannow to check for damaged missing files. If that fails try a repair.
Removed sound card Removed second Hard Drive Disconecetd one dvd Took out 2 gig ram Removed one graphics card Still just switched off Tried graphics caed in other slot then tried the other card in both slots. Swapped ram to othe slots then tried other pair in both.
Tried with other DVD drive.
All psu cables new.
Monitor only 2 months old and works fine on second pc.
If you are certain that physical dermination isnt the cause, and i could even suggest that the bios battery or its memory may be at fault, removal and replacement can determine that.. but caution is required, and knowledge, then it comes down to software. Drivers,particularly the graphics card.
when the system is rebooted, are there any error messages in in the control panel- Admin Tools - event viewer?