monitor display problems

My computer display screen has been acting strange off and on. When I boot it up the screen image is really strange. On the log-in screen there is a circle in the left hand corner. When I do log on, the image I see on the screen has blocks on it. Like rectangular bricks sort of. I don't know how to describe it. Do I need to update my video card or something? It just doesn't want to go away!

My comp is still acting funny. The display screen is completely distorted with lines and stuff all over the screen. I tried hooking it up to another monitor but it's still all distorted and strange looking. I can even see anything. It's all screwed up. my comp is a dell windows xp, it's not that old. Can someone tell what the deal is?