I had something similar happen and i tried swapping boards. I ended up putting the original boards back together and it worked.
originally i only reseat the boards for audio issues, but then i got graphic issues like you.
i kinda just had to press firm and really sandwhich them together a few...
Also I wonder if thats whats wrong with my friends ST board lol.
its mounted to the inside of the cab vertically lol
he would occasionally smack the side of the cab (where its mounted) to get it to work again lol!