I agree with Ed that this sounds more like a memory problem. In addition to Ed's comments, ask your client if he is using the memory chips from his old machine in his new machine. If so, that may be your culprit. I had all sorts of BSOT problems with the machine I bought a few years ago due to one of the memory SIMMs being bad. It never hurts to try replacing the memory chips with ones you know work to see if that resolves the problem.