Have you tested your RAM? I had a similar situation where I had upgraded my memory and everything worked fine until I went to play Quake3. Also running Linux

Have you tested your RAM? I had a similar situation where I had upgraded my memory and everything worked fine until I went to play Quake3. Also running Linux was miserable while Windows seemed to work ok. I finally figured out it was a bad stick of RAM and it save a lot of frustration.