Grainy computer monitor

[thedamndest]

Here is the situation. I have an old laptop that is now hooked up to an external monitor because the screen on the laptop died. I don't know why the screen died, but it just flickered and went out one day. But now when I hook that same laptop up to the monitor the picture is grainy and colors don't look right. I downloaded a new driver but that did not do anything. I'm out of things to do.