Problem with adding computer to domain.

After “succesful” upgrade from NT 4 to WIN2000
Server all seems to be OK except I can not add new computer to domain. All old computers can login to domain (win98, W2K etc) and working properly but new, just bought machine running W2K Pro can not be added to domain. Vague error – due to networking problems your computer cannot be added t domain. Cables are 100% OK. Computer also is set to obtain IP from DHCP server and receives all settings OK.
Any idea why?
Cezar