Sounds like a partially buggered GFX card to me. I've had one before that worked fine in 2D (Windows etc.) but the 3D rendering hardware developed a fault after about a week and I started getting weird graphics glitches.
P.S. When building a new system, I always figure in a 'bedding in' time after the machine is built. There always seems to be some problems that have to be addressed after the build. This usually involves having to return one or two faulty components. I'm no longer surprised when a piece of kit arrives DOA. Mind you, I haven't built a PC for several years and have no plans to build one in the future, frankly. My nerves can no longer take the stress. :)
P.S. When building a new system, I always figure in a 'bedding in' time after the machine is built. There always seems to be some problems that have to be addressed after the build. This usually involves having to return one or two faulty components. I'm no longer surprised when a piece of kit arrives DOA. Mind you, I haven't built a PC for several years and have no plans to build one in the future, frankly. My nerves can no longer take the stress. :)