If you have admin rights I would set up a user account on the local machine with a known pass or no password at all. Make sure and give the account admin rights.
Log off to test the account. at the ctl alt del screen click the more options tab and change it from a domain login to a local machine login. see if you can get in with the new account.
You can either continue to log in with this account to the local machine or you can remove the computer from the domain and add it to a workgroup instead.
Be careful and make sure you can access the computer locally before you remove it from the domain as when you do this you will loose the user account that is set up now.