Can’t login to 5.1 server

We recently installed a 5.1 server. After installing it had run for a few days with no problem. Last Monday the server hung. Had to power off and on because it was locked tight. Since then we have not been able to log into the server even with Adminusing client 3.01 sp1 on a Win95 box. Using NT or a later version of client works. I know this sounds like an easy fix(upgrade the client) but we would like to know why ut did this in the first place as this server is not in production yet and we wouldn’t like this to happen after loading all the users and etc. any ideas?
Thanks,
Gary Wilson