A windows 2000 Domain user cant access NT4

I have an user with a Windows Xp notebook who i setted up on a domain (Windows 2000 server).With the same username and password he used in the past to access his NT4 file server. The Ip/WINS/DNS/DGateway is correct.I see the ntserver on the network but cant access it due to username and password it requested. Please advice Thanks

Frank Simon