cannot connect to sql server in single user mode

I have started my SQL Server 2008 sqlcst02\inst01 in Single User Mode by appending the ;-m to the end of the startup parameters for this instance in SQL Server Configuration Manager. I have stopped SQL Server Agent for the inst01 instance. My account is a member of the Domain Admin group and I have attempted to login using sqlcmd -S sqlcst02\inst01 and keep getting an error that the service is in Single User Mode and only one administrator can be logged in. I tried adding ;-m"sqlcmd" to the startup parameters to limit the connection to just sqlcmd but I get the same results. I have tried this logged in as my own account and logged in as the local administrator account. I have started the command prompt as myself and as administrator but I get the same results. I have tried connecting using ADMIN:sqlcst02\inst01 in SSMS. No luck.

I'm attempting to reset the sa password as none of this information was left for me by the previous admin. This is maddening. I've done this before on other machines with no issues.

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.

StackExchange Database Administrators Q#31660, answer score: 6