Memory. Northbridge overheating. Crap drivers. Any number of things. If you're running windows check to make sure that when there's a BSOD the computer stays on and displays it.
You can start with the memory, sure. I personally have had a pretty ridiculous amount of sticks fail on me lately (all brands, different boxes). I had a similar issue after installing the latest X-Fi drivers on one workstation. I had system resets because of a failing video card even. You never know. Programs and general tips are in the FAQ below: