It is asking you to log in using either an account defined on the local
computer, or an account defined on a domain. Since you've destroyed the
link to the domain by moving the machine out of the domain, your only option
is to log in with a locally-defined account.
By default, this account is created on every computer and is called
"administrator". It's always worth trying to log in with a blank password
in cases like this (just in case your system administrators are dumb).
At some stage, you will need to ask your network guys very nicely to join
you back to the domain, so rather than risk further damage to your machine,
it's best to go straight to them and tell them what you've done.
Regards
Oli