Disable automatic restart on system failure
If your computer has ever randomly restarted for no apparent reason, it could be experiencing a system failure, when the computer encouters a problem which it cannot fix. By default it is set to automatically restart on system failure but it is possible to change it so that it will display a blue screen with error information instead, which you can use to solve the problem. To do so, complete the following steps, depending on your operating system.
Windows XP
Go to Start > Run > Type sysdm.cpl > Press Enter
In System Properties, go to the Advanced tab and click Settings under Startup and Recovery.
Uncheck Automatically restart under System failure and click OK out of both windows.
Windows Vista / 7
Click Start 
> In Start Search, type sysdm.cpl > Press Enter
Click Continue if you encounter the following prompt.
In System Properties, go to the Advanced tab and click Settings under Startup and Recovery.
Uncheck Automatically restart under System failure and click OK out of both windows.
Now, in the case of a system failure, the computer will display a blue screen containing error information like the following, instead of restarting. You can use the information on this screen to diagnose and solve the problem.
