if the pc only has domain accounts on it then you cant do anything with it other than reinstall the OS.
this is because you need the domain controller to authenticate the logon, no DC no log on..
the pc however should have a local account, this is the account that is created when the pc is installed and before it goes onto the domain.
it may however be setup to not show the local account, if it is then you can logon to it using the administrator account, but you will need the password.
if you dont know the password then do a google search on removing passwords under the relevant OS, there are a few ways.
really though the easiest thing is to reinstall the OS.
