Overheat due to faulty / blocked fans
Household power surges fridge etc switching on/off
faulty memory stick try memtest click here virus or spyware scan for both especially if shutting down with in a few minutes of switch on or internet use
driver conflicts especially graphics cards get the latest drivers for your equipment
When Running windows and it crashes you will get a blue screen and it will automatically restart, often it will restart too fast for you to see the error message. To disable auto restart on system failure, so you can see the error message.
- Go to Start -> Control Panel -> System (Windows+Pause works, too)
- Go to Advanced
- Under the Startup and Recovery section, click Settings...
- Under System Failure un-check "Automatically restart"