I've seen and had similar issues on computers before and to me it sounds like your graphics card is having problems, most likely with the vram. This could have been caused by a number of things such as the card overheating and being damaged or faulty vram or other components.

If you can, try returning the card and replacing it with another one to see if you just ended up with a bad video card. If this problem still occurs then it could be a sign of a much larger problem such as motherboard failure. At this point if you are not familiar with setting up and working with computer hardware yourself, you should take it to a repair place and see if they can help you.