access a server w/out known id or p/word

Upgrading the NIC in my file server failed while trying to add TCP/IP.

Now the server is in its own workgroup and I do not know the original userid or password to gain access to network applet or control panel.

I cannot get past the logon screen.

The usual id and password fail, my workstation id and password fail.

Can I somehow insert via dos a new id and password or is there a backdoor userid to at least open the server ?