Win.2000 Pro. logon problem

I have a thinkpad with a 2000 professional OS running. I made changes on my domain name, userid and password; when trying to logon after restarting, I am getting message stated that my domain and userid not correct. I am positive that I have been putting the correct domain and userid and password. I am unable to logon into the window logon screen. My only solution is to reinstall Win2000 Pro and that will have to partioned and format my hard-drive. How can i get into the system without loosingmy data?…Please someone help me.