workgroup network

I have 4 computers in workgroup network and one 2003 server. when from 3 computers try to connect to the server share drive so they can connect but from 1 computer when I am doing same thing so it is asking for user name and password to access that share drive on server. All 4 computers configuration and OS is same. can u pls. answer me how can I resolve this problem? I have done MCSE & CCNA but still I could not solve this problem. pls. reply me.