Check out Memtest. http://hcidesign.com/memtest/download.html
But first rt click MyComputer>Properties>Advanced>Startup and
Recovery-Settings>Uncheck Automatically Restart.
Next time you have a problem you should get a blue screen with error
message. Post the message here. If it says
IRQ_Less_or_Equal Than it might be your graphics driver if you are using a
Nvidia graphics card. If that's the
case go to www.guru3d.com and download and install a different driver.
Uninstall the old one first.
