Hi
If you don't see any error messages, right click on My Computer, select
Properties and then the Advanced tab. Click on Settings under Startup and
Recovery and disable 'Automatically restart'. Next time your PC reboots,
you should see a Blue Screen. Could you please post the Stop Code from the
BSOD?
Also, please have a look in the Event Viewer to see if any entries there may
refer to the problem.