What can you see? Are there gray squares, or what. If you are seeing just gray squares it could be a corrupted monitor profile. Try switching to an sRGB profile and see if that fixes the problem. Otherwise, I have no idea. Perhaps others will be of help.
Just another thought. Are you sure Camera Raw installed? In Photoshop, go to Help/about Plug-Ins and click on Camera Raw. It should display a dialog indicating what version of Camera Raw is installed. If you just installed the master collection, then you probably have version 6.0, and you should upgrade to 6.3. However, the D200 should be supported, and you should be able to see your raw images if Camera Raw is properly installed.
1. I see, instead of thumbnail, a white square with NEF letters on blue background on left upper corner.
2. Camera raw plug-in is 126.96.36.199
What is your operating system?
What is the exact path to where Camera Raw is installed?
Is there more than one version of Camera Raw on your system?