Administrator "insufficient rights"

I have had a PC (one of two) on a temporary network with a DC controller.
Both PC's are now back in peer to peer mode.
On one of the PC's I cannot change the IP address as I do not have enough
rights and I need to contact my administrator (me). I have tried creating
other admins, all with the same result, neither will it work with the built
in administrator's account.
I don't know if this problem existed before the promotion but it does now.
TIA
TWK