Best way, if there are no hardware issues with RAM or the motherboard or the video card causing this, re-install Windows. If you don't want to go that way, you need to try to swap out the RAM for a good stick, and test things again. Maybe uninstall and re-install the drivers for the system, do a BIOS update, run a virus and spyware scan.
When the crash happens, it should tell you what caused it, usually it's a driver file, get that info from the screen and post it.
Re-installing Windows is a much easier path to take really.