Hi - new to this forum so treat me gently! I have a bit of a problem with my Mac Pro. The screen flickers intermittently then locks up. This can be anything from a couple of minutes after starting - to 40 minutes later! Its never done anything like this before. I'm running 6 Gig of RAM - so I don't think its a memory issue. I've tried swearing at it - but to no avail! Any help would be gratefully received!