Strange Problem with T21 Monitor / Video card - Help

[Ari]

Hey everyone I'm new here, and unfortunately I was driven here by a problem. My T21 starting giving me some problems recently - sometimes when I turn it on image only appears in the bottom right quarter of the screen - the colours constantly fluctuate and lines appear and move around.

But if I restart my computer a few times, everything will just load up fine no problem, and the screen will work perfectly until I shut if off.

Turn it back on, and the problem returns. Sometimes.

Very strange any ideas what causes this sort of thing? It just started out of hte blue too!