Lost administrative rights on upgrade to 7.10

[J Reeves]

Hello from Labrador

I was using Ubuntu 7.04 happily enough for several months, logging into
root when I needed up get updates or add programs etc, and using a
separate account for everyday use.  This everyday account did not have
any administrative rights, not even with su or sudo.  root was my only
administrative account.

Yesterday I upgraded to 7.10, and now when I get the login screen and
try to login under root, as I used to do occasionally, I get the
message,

"The system administrator cannot login with this screen"

Computer still works fine in my limited user account but I cannot use
sudo.

What to do?

Jojo