Admin Pswrd gone after remove frm domain

I have an XP pro PC setup as member of an NT 4.0 Server domain. I removed the PC from the domain and added it to a local workgroup. XP asked for an administrator account and password to remove it from the existing domain. I provided the administrator account and it was accepted and said I needed to reboot the system. When I did, I can no longer login as administrator. The password is invalid? The message syays the user acount/ domain/ or password in wrong. I have tried several variations such as workgroup\administrator and tried the old password and tried a blank password. I have checked caplock etc. Any help would be appreciated. I don’t want to re-install XP unless I absolutely have to.
thanks
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