File Protection & Restore Problem

All of suddent, my PC pop up a box, said, “Files that are required for windows to run properly have been replaced by unrecognized version, To maintain system stability, windoew must restore the original version of these files.”, “Winkdj.exe has generated errors and will be closed by windows. You will need to restart the program”, same thing with the OSD.exe file. I had tried to restore WIN2000Pro, but it will erase all the data. Is there other way to restore the OS without losing all my data? Can anybody tell me what’s going on with my PC, and solution to my problem or recommend me some sites that can help my problem? I’ll appreciate any suggestions & advices. Thank you!