Or you could highlight all of your pictures, right click on them, then select "refresh thumbnail". I had the same problem and this is the only thing that fixed it. Disabling XPs thumbnail cache and deleting the thumbs.db file wouldn't work for some reason but the right click did.

 

i speicalize in MS Paint h:

 

lol yeah it wasnt the best PS ive ever seen pat but hey.

anyway. yeah. right click on the pic and select 'refresh thumbnail'