Lost thumbnail previews?

[gsh]

I'm using ME (yeah, I know I'm a glutton for punishment) and have just installed Adobe Photoshop 7.1, replacing v5LE. Since switching, I no longer get the thumbnail image preview below the attributes pane when I click on jpegs or gifs. I still get it for bitmaps. I also no longer have thumbnail previews if I set the icon view for thumbnails.
I can set the folders with my image files the same as My Pictures folder, so I have that god awful huge image preview box, but it is unsightly and doesn't help me with images on disc.
Even saving a jpeg in photoshop with the preview box ticked does no good. However, if I change a jpeg extension to bmp, lo and behold image preview works as before (but obviously that's no good as the files then get an error message when trying to open). It must be an association with the file extension that has been changed somewhere, but for the life of me I cannot work out how to fix it.
Any help would be appreciated.

[Capmaster]

Try opening explorer and under tools, open folder options, then file types. Find "JPG File" and see if Photoshop is the application registered for it. If not, click "change" and point it to Photoshop.exe in the Adobe folder.

Sometimes graphics programs glom onto an extension when you install it and set their own app as the default app to open it. Some apps are polite, like Photoshop, and ask you if you'd like to change the file association, but some don't. You have to go in after the install and change it back.

That should do it unless something else is going on.

[gsh]

Try opening explorer and under tools, open folder options, then file types. Find "JPG File" and see if Photoshop is the application registered for it. If not, click "change" and point it to Photoshop.exe in the Adobe folder.

Thanks for your reply. This was the first thing I checked, and Photoshop is indeed the registered app.
Under this list it states that bitmaps are customised, but I cannot find a way to determine what this customisation is to try and apply the same to other image files.
Any other ideas?