[Fyron]

System Properties (right click on My Computer and select Properties) > Advanced tab > Startup and Recovery, disable "Automatically Reboot." From the blue screen, you can almost always see what the problem was, in a roundabout fashion. There will usually be a driver file listed, which you can track down to see which piece of hardware is causing the crashes (if it is a hardware problem).

Every so many months, I seem to get random reboot problems lasting for a few days, which inexplicibly disappear. I have never been able to figure out what causes them.