Video cards on these are a common failure point, especially on mpu's that haven't had the correc airflow cooling off the video card. But the adastra board on these fails as well (that's the other board with the cpu and the memory on it). Only way to know is to replace the parts to see which one has failed. If you don't have spare mpu (or the owner doesn't), I would suggest getting one while they are cheap and relatively easy to find, because parts will eventually dry up and if you don't have spares, fixing them will cost a lot more.