Overclocking a GPU can cause that. Before I upgraded, I had a 6670 I would OC and if I pushed it too hard it would start with red lines or blocking.
If overclocking, try playing w/out the OC.
Try installing and enabling Gopher's IHud mod. Fixed ? Try reinstalling the game. Not fixed ?
Try reinstalling the game.
If problem persists on a clean install with no mods, potentially a driver issue/conflict with Skyrim. If same thing occurs on other games or watching video, likely a hardware issue.
I had a flat screen TV that started doing that before it failed. The convergence was off. Google "convergence". It did it on more than one application though.
I would highly recommend you check out the nexus forums for Skyrim only problems. If you are new to it, highly suggest you google "Gopher Skyrim Mod Sanctuary". He has a beginner's guide of videos on YouTube that will help you eliminate 95% of potential problems.