My computer keeps rebooting on it's own

Hi, I am having trouble with my girlfriend's computer. Often when she is working on something like sending an email or surfing the internet, the computer just turns itself off and reboot. This is happening a lot lately and need some assistance of what may be the problem. Help!!!!!!

Turn off Automated Restart so that the machine will "stop" on a BSOD with an error message that will give you some clues as to what is happening. These system failure errors are usually isolated and occur randomly. As such, the best way for the operating system to deal with them is to automatically restart. However, you can disable the automatic restart behavior. Follow these steps: Go to Start/Control Panel/System/Advanced/Startup&Recovery(Settings). In the System Failure section, deselect the Automatically Restart check box, and click OK. To re-enable just reverse the changes later after you have the probelm solved. You can also look in Event Viewer to get errors and codes of events surrounding the time of the problem. Click Start, and then click Control Panel. Click Performance and Maintenance, then click Administrative Tools, and then double-click Computer Management. Is this a Laptop? how long has it been since you've cleaned out the dust bunnies inside of the tower or case? These kinds of problems are often "heat" related. Best Regards

Thank you for your response. How do I turn off the "Automated restart"?

See edited post above.

I have a desktop and cleaned the dust from the fan on both the CPU and outer fans. I will try the procedures as indicated above and will give you an update afterwards. Thank you.