Delete your Thumbcache files with the Disk Cleanup Utility (Press Start, (My) Computer, Right click C: Drive (your Main or System Drive), Properties, Click on the Disk Clean Up button). Thumbnails is one of the options you can choose to clean up.
Then delete your (hidden) IconCache.db which you'll find in C:\Users\Your User Name\AppData\Local folder
Finally re-start.
That may (only may) cure it.