Help! -user account

I am servicing a customer's PC. They have a network with a domain. I took the PC to my workshop and logged on to the computer with its local administrative password. I wanted to run some tests so I changed the networking from domain to workgroup and put it in the workshop's workgroup. After rebooting, the local admin password I used does not work! Please help me!

Im thinking of reinstalling windows but hope there is a better way.

That is because:

• You have chosen the wrong domain. Choose "local" at the login screen
• Make the local-password equal to the domain pass-word.

No man, remember I changed networking to workgroup. I dont have the option to choose between domain ot local computer.