This could be any number of issues (As we don't know much of your configuration or video card, etc)

The easiest way would be to make sure any of the current topics can't help you (Like the Radeon Video Card specficially)

Also if you are still having problems, turn off Animated Backgrounds. Dom2 eats alot of memory with them on and it may be your system (Depending on your memory or drivers or whatever) is having issues with that aspect.