Hi there,
I'm not sure what is going on with your Graphic Card but a fairly easy way to see if it is a hardware problem or a software one is to run a live version of Ubuntu or another Linux Distro.
If the card works fine when you do this then, it is a more than likely to be a problem with the software environment in Windows. However, if the graphics are pixelated in Linux then it is probably a hardware fault.
Another quick test is to see if the graphic card works OK in BIOS before Windows installs. If everything is fine here then, once again it is more than likely to be a software problem rather than hardware.