Something to try and solve your problem.
Do you have Nero installed?? If so try uninstalling it and see what happens.
If you want to use Nero, you have to go to
C:\Program Files\Common Files\Ahead\DSFilter\
Then rename the following items (if they exist) from .ax to .old, as this will prevent them from being accessed:
- NeVideo.ax
- NeroVideoProc.ax
- lmpgspl.ax
This will prevent some of the Nero codecs from rendering video thumbnails, which is most likely the cause of the problem.
If you do not have Nero installed, try control panel, then folder options, then view and tick "Always show icons, never thumbnails".