Make Random Reboots Tell You What's Up
There you are, working at your computer, minding your own business and doing nothing untoward, when suddenly--bam! The system starts rebooting. If you experience random reboots that have no discernible cause, here's a little trick that might take you a step closer to solving the mystery. In Windows 2000 and XP, right-click My Computer and choose Properties; click the Advanced tab. In Vista, click the Start button, type System, Properties, Advanced, and press Enter. Click Continue if prompted by User Account Control.
In all versions, click the Settings button under 'Startup and Recovery'. Uncheck the Automatically restart box, and click OK twice. The next time the problem occurs, instead of rebooting you will likely see a text screen reporting a system error. Jot down any information it contains and see whether you can find related information from your favorite support guru or Web site.