You are sort of vague in the description of your problem. Is it the Bridge that can't show the thumbnails, or are you saying that when you do File | Open, that you can't see a thumbnail at the bottom of the dialog, or that you can't choose the thumbnail option of the dialog, or what? If its Bridge, then the cache was probably lost to and you need to rebuild it. I'd use Bridge preferences to set its location (usually better on a 2nd hard drive, and not in My Photos. I use a variety of other file browsers, but often use Bridge and find it quite adequate and it allows a very powerful and fast workflow for RAW conversions (as I've detailed in a tutorial in the digital forum). But for just dealing with one photo at a time, I usually use BreezeBrowser Pro.
"The map is not the Territory"