The problem is that all of the preview thumbnail images used in the icons are stored in a cache file, which sometimes goes all wacky and gets corrupted, and requires some cleanup.
Fix the Problem with Disk Cleanup
To fix the problem, simply open up Disk Cleanup by typing “disk cleanup” into the start menu search, or find it under the accessories area. You can run a full disk cleanup if you want, but if you just want to quickly fix the problem, scroll down until you see Thumbnails and make sure that one is checked.
You’ll want to click the “Clean up system files” button, wait for it to finish, and then probably log off and back on.
Everything should be looking good now. Did it solve the problem for you?