I don't think you will be able to login with your domain account after the workstation has been removed from the domain - there is no way your credentials can be verified. You'll have to log on using the local administrator account, create a new local user account and then copy the profile from your domain account onto your local account via system properties.
Someone correct me if I'm wrong...
Lukas - are you trying to use a local or domain account, and what is the error message you get when trying to login?