cannot connect to sql server in single user mode
Another alternative to recovering access to a SQL Server is outlined in this article, and doesn't require restarting in single user mode:

http://www.mssqltips.com/sqlservertip/2682/recover-access-to-a-sql-server-instance/

Essentially, download PSExec, then run it with the following command line (fill in your location of SSMS.exe):

PsExec -s -i "C:\Program Files (x86)\...\ssms.exe"


You will be prompted to connect - the authentication mode will be Windows auth and hard-coded to NT AUTHORITY\SYSTEM. Once connected, you will be able to go into security and fix the sa password, add yourself as admin, add other admins, etc.

The article above has several caveats you should read before trying this, and you may also want to review the comments at the bottom.