Since you're getting a stop error, it's likely to not be an issue like an overheating CPU or bad PSU. RAM can do this, and a variety of other things related to Windows. A bad hard drive can also do it, especially if you hear a click or clack when the system stops.
Memtest86 will rule out any RAM problems, but it does need to run for 6-8 hours to be sure. If it is RAM, it might show up pretty quick, so if any errors are shown, you can stop the test and start talking to your RAM.