You need to follow the steps described in Troubleshooting: Connecting to SQL Server When System Administrators Are Locked Out and add your own Windows user as a member of sysadmin:
-m
and -f
startup parameters (or you can start sqlservr.exe -c -sEXPRESS -m -f
from console)sqlcmd -E -A -S .\EXPRESS
or from SSMS use admin:.\EXPRESS
create login [machinename\username] from windows
to create your Windows login in SQLsp_addsrvrolemember 'machinename\username', 'sysadmin';
to make urself sysadmin member-m -f