HELP!!!!!! Dell studio screen problem!

My screen frequently messes up! the screen starts to flicker and then the screen will either go blank except a small strip at the top of the screen which is just a bunch of mixed colors. Like this:

Or it will get these 5 columns with horizontal lines through them. Like this:

It does this very frequently and is EXTREMELY annoying! The only thing I can ever do is to turn it off and then on, but after some time it does it again. IT DOES NOT HAVE THIS PROBLEM IF IT IS PLUGGED INTO AND EXTERNAL MONITOR. I haven't got the slightest clue as to what's wrong. My warranty is up and it has been doing this since I got it. (It is refurbished) I sent it in and they sent it back saying it was fixed but it wasn't. And I just never sent it back. But now it does it more than it used to. PLEASE HELP!