Cannot login to Windows 2k domain

I have a LAN with Win 2k as PDC but clients are mixture of Win 2K,Win NT and Win98. The problems is i cannot log in with win 2k clients and the error generated is “there is no loggon servers to service request” but i can ping them from every where. But with Windows NT there s no problem. I have put Service pack 4 in the win2k pcs.so ican see where the problems is from.