Errrr.... What? Were you having problems before the clean install with new/different cards? I've never heard of that.

Is the restart problem only happening when mining?

"Random" restarts or program exceptions, generally the first thing you want to look at is the RAM, both because the sticks are prone to being the first component to fail, and because it's super-easy to take all out but one, and if the problem persists, try one of the other ones.