jpg files thumbnails loads too slow

i am using win 7 pro. 64 bit sp 1
HP E7500 2.93 Ghz , 4 gb RAM , 1 gb nvidia Graphics card etc.,
whenever i am trying to browse the folder which contains all jpg files, thumbnails takes extremely long time to load, and i have to open preview one by one photos. After a lot about 200 or more previews i can reach on desired one which is embarrassing. My jpg files are stored in a network shared folder in NAS.
NOTE : i have tried as follows:
folder option , choose visual effects for best performance , clean boot and tried to delete thumbs.db (cache of thumbnail) but it couldn't delete, and i thought if it can so it won't make any difference.

So... What's the question?

I take it you want to use the thumbnails, and want to speed up how quickly they're viewable?

An SSD would probably help, along with other faster computer components.

Have you tried clearing off the clutter on your pc? This includes removing old unwanted files, temp folders, defragging, registry cleaning and the lots.

Thanks all of you to pay attan. and give time i have reset thumbnail cache through registry as brink sir suggested its a game of thumbnail cache in my case its been disable however and so i have to reactivate it.

i have clear the thumbnail cache through registry settings.

here is a link below:

Thumbnail Previews - Enable or Disable

but before applying registry key to first disable and then enable it is strongly advisable to create restore point of windows os, and take registry backup.

once thumbnail cache has enabled, the size of thumbs.db increases as you open image files.

thanks once again all of you to pay attn. and your time.

Regards SKumar.