Right-click on the My Computer icon on your desktop, choose Properties, click the dvanced button, click the Settings button in the Startup and Recovery section. In the Sysyem Failure section, untick the Automatically Restart option, click OK, Apply and OK to exit. Now when Windows should give you an error message rather than restarting, What is that error message. It's sounds like some sort of conflict, either Hardware or software. Have you installed anything recently, a new drive maybe or some new software or driver update?