Son has a situation...using a very, very old but large PC tower, and, after getting a new GPU last week, the system doesn't want to start..and stay started. It will start, shut-off...try to start again and then won't start at all until we fiddle with some things. I finally took the board out of the case, put in the new GPU and it's running like a charm. So, what would be the most suspicious culprit: The case or the mobo? The mobo is a 6 or so year old Gigabyte board. I have one similar and I do like mine.