In some configurations, SSMS will attempt to make several connections. Multiple connections will fail because SQL Server is in single-user mode. You can select one of the following actions to perform. Do one of the following.

1. Connect with Object Explorer using Windows Authentication (which includes your Administrator credentials). Expand Security, expand Logins, and double-click your own login. On the Server Roles page, select sysadmin, and then click OK.
2. Instead of connecting with Object Explorer, connect with a Query Window using Windows Authentication (which includes your Administrator credentials). (You can only connect this way if you did not connect with Object Explorer.) Execute code such as the following to add a new Windows Authentication login that is a member of the sysadmin fixed server role. The following example adds a domain user named CONTOSO\PatK.
   CREATE LOGIN [CONTOSO\PatK] FROM WINDOWS;
   ALTER SERVER ROLE sysadmin ADD MEMBER [CONTOSO\PatK];

3. If your SQL Server is running in mixed authentication mode, connect with a Query Window using Windows Authentication (which includes your Administrator credentials). Execute code such as the following to create a new SQL Server Authentication login that is a member of the sysadmin fixed server role.
   CREATE LOGIN TempLogin WITH PASSWORD = '************';
   ALTER SERVER ROLE sysadmin ADD MEMBER TempLogin;

   Caution
   Replace ************ with a strong password.

4. If your SQL Server is running in mixed authentication mode and you want to reset the password of the sa account, connect with a Query Window using Windows Authentication (which includes your Administrator credentials). Change the password of the sa account with the following syntax.
   ALTER LOGIN sa WITH PASSWORD = '************';

   Caution
   Replace ************ with a strong password.