User guest does not have permission to run DBCC checkprimaryfile

We recently upgraded our server to a new machine and Server 2012.  In the process the domain name was changed.  Now when I try to attach a database in ssms on my workstation I get the above error.  I still connect to ssms to the same SQL Server on my workstation using Windows Authentication but now with my new User Name of ELDERS/brad whereas the old User Name was ELDERSBDB/brad.  ELDERS/brad has full administrator permission on this workstation.  Why does ssms consider me a guest and how can I change it back to sysadmin 

Thanks for any help

BHend