MFair make sure you install the skins from our website for UE, if you use an older skin pack with UE you may be missing some as more were removed from the default install for UE to fit on DVD etc.
If you are using the latest pack then something is screwed on the PC, or something interfered with install of skins, and maybe WOFF. AV?
Check disk for errors, if overclocking turn it right down or preferably off (run at standard/default speed)to test. That can also affect GPU and its output and memory (random issues).
Check the troubleshooting in FAQ.