|Just to make certain, did you set the folder view to Thumbnails?|
If not, right click in your picture folder in an empty spot and click View>>Thumbnails.
If so, I have no clue. How many pictures do you have in that folder? Perhaps it's many and it would require your computer a little more time to load the pics? Try making a new picture (make one in paint or another photo editing program) and save it into a New Folder and try to view it as a thumbnail. See what happends.
Abit AN8 Socket 939
AMD64 3000+ -1.8Ghz
Corsair 1Gig Dual-Channel 2x512
MSI Radeon x800 PCI-E 390&700@441&990
Seagate 160Gig SATA
WD 80Gig SATA
Antec TrueControl 2.0 550 Watts