I would check all the sql and cluster services and make sure the password is good. Did the node get evicted from the cluster group or does it show as offline? If it is just off line it may be possible to just correct the logins and restart the server. If it has been evicted, I don't know you may be able to re-add it from the cluster administrator like you would any other win2k box I don't know what it would do to sql at all.

Wes