login problem in 2003 domain server

I’m having problem login to my domain server after expering user’s id password my clients using windows 98. i have create new user id in server & try to connect with that user id it doesn’t allow me to login. but it allow to login with other’s user id. but with my user id or newly created user id even the administrator id can’t login to my domain why it is happening anybody can help me same. thanks