Changing from a Workgroup to Domain

Hi,
Domain name:saftsng.
Server: Win NT
Workstation: HP Notebook with Win2k Professional.
The issue is that the notebook, all of a sudden was not able to connect to the network. On checking the settings, I (by mistake)changed (my computer–rightclick–>properties–>network identification–>properties) from domain to workgroup (xyz). Later, I am trying to revert back
to the domain,I am not able to do it and get an error message”The dpecitied domain either does not exist or could not be contacted”.
But I am able to ping my default gateway, DNS server, etc.

Any help to revert back to domain saftsng is most appreciated.