I'm having a similar problem.
My linux pc keeps crashing in one of two ways after a recent update. One it will just reboot on its own. Two, the screen will get distorted and freeze. I had a similar issue about two years ago and it went away after an update. It basically has become un-usable and crashes every few minutes now.
I'll give the nouveau driver a try, since I have an nvidea 6500. Not sure if it works yet.