my pc closes down automatically

[Guest]

if i am using it all is fine. if i walk away from it and return a short while
later i find that the pc has rebooted itself. any ideas / help appreciated

 

[Mark L. Ferguson]

Disable automatic restart on system failure (on SP2): Press F8 on restart,
and see the menu item to disable auto restart. Restart, and when the STOP
message appears, record information needed for further troubleshooting.