pc problem

you may have two possible problems :
Bad memory- it may be that some of your memory is going bad
Bad fan- the processor is overheating and shut off

The first thing to do is to right click on My Computer to open the system properties dialog box, click on the Advanced tab, click on Startup and Recovery, and then untick the Automatically Reboot option.

That will at least give you an error screen that may enable you to troubleshoot the problem.

Alan

Another thing is One of the Sasser viruses created in Feb or march was a big reason for alot of people turning on and off. Do you have anti-virus and is it up to date. Also intalling critical update for windows is also recommended.