hi

my computer screen just jumps in and out concave and convex I think the more settings are wrong,
it was stuck on 400x640, I then changed it to 600x800 but it still jumps.

any suggestions

thanks

It sounds to be most likely a monitor gone bad. It does not sound like a video card issue to me with what you described. The way to know for sure is to replace one or the other. I would borrow a monitor if possible as this would be the easiest way to narrow the issue down without having to open up the PC and deal with installing drivers.