Hi guys, In order to fix this you have to follow the next steps:
1. First then all, Stop SQL Server from Sql Server Configuration Manager
2. Then, Open a CMD window (as Administrator), execute the following command and don't close this window:
"c:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\Binn\sqlservr.exe" -m -s SQLEXPRESS
3. After that, just open a new CMD window (as Administrator) and run the next command:
sqlcmd -S .\SQLEXPRESS
Then, we need to assign the sysadmin role to your user, executing the next 2 lines:
3.1. sp_addsrvrolemember 'YourDomain\YourUserName', 'sysadmin'
3.2. GO
4. Now, go back to first CMD window and press Ctrl+C and Y (yes) to shutdown SQL Server. Then, you just need to start SQL Server from Sql Server Configuration Manager. Log into Management Studio, go to Security / Logins and the user you use should be a "sysadmin."
