If you shut down your Windows XP-based computer, your computer may restart instead of shutting down. The computer may also restart unexpectedly while you are using the computer to perform certain tasks. A error message on a blue screen may appear when the computer restarts. CAUSE
This behavior may occur if Windows throws a fatal error during a typical operation or during the shutdown process. By default, the computer is configured to automatically restart during a fatal error. To view this setting, right-click My Computer, click the Advanced tab, click Settings under Startup and Recovery, and then view the Automatically restart check box under System Failure. If the Automatically restart check box is selected, Windows automatically restarts if the computer stops unexpectedly. RESOLUTION
If your computer constantly restarts if you are using the computer or if you are trying to shut down the computer, click to clear the Automatically restart check box. If you clear this check box, you receive an error message if a stop error occurs. This error message may describe the cause of the critical stop error. You can also review the system log in Event Viewer to view the critical stop error that occurs when the computer restarts.