XBMC on Ubuntu Video Problems

I have XBMC running on Ubuntu, which has been working perfectly for over a year now. All of a sudden, the screen freezes up and I get funky colored blocks all over the screen. Some times I can restart the PC and it will allow me to watch a movie and sometimes not. I was leaning towards a video card issue but I dont know how to diagnose it. I am not very familiar with Linux, so trouble shooting can be kinda tough for me. I was hoping someone here may be able to help me out by telling me how to determine if this is a video card issue with out purchasing a new card first. I have recently updated the machine to the latest Unbuntu version in hopes that it would fix the problem but it did not. I have been trying to find the magic command line to update XBMC but I dont see it in the wiki. Not being familiar with Linux I probably have over looked it.

Thanks,

David

Funky coloured blocks is either a video card issue, or possible related to overheating. As an easy first check, check the inside of your box and the gfx card for dust build-up and other muck. Then, check temps when running; you'll have to wait for someone more knowledgeable than me to tell you how