Or it could be any other random bad hardware. Start with a memory test program first, as it doesn't involve needlessly buying random parts. You can make a bootable CD-ROM or bootable floppy via that link. Let it get to Pass: 5 before hitting escape. It should take up to 2 hours to get that far.
Also, what kind of crash is it? Does the program crash? Does Windows reboot instantly? Is there a blue screen of death?
Configure your computer to create crash dumps:
Start > Run > control sysdm.cpl,,3 > Startup and Recovery > Settings > uncheck "Automatically restart" and set "Write debugging information" to "Small memory dump (64 KB)". The dump directory is usually set to %SystemRoot%\Minidump
If you find any files in C:\WINDOWS\Minidump after getting a blue screen of death, PM me and I'll tell you where you can email them so I can debug them and find out what's wrong.