At times it is needed to reset the SA password for SQL without knowing the existing SA password. For instance, the Administrator that setup the SA password leaves without giving the Credential information.
I)Make sure that the instance is in Mixed mode and not Windows Authentication.
This can be changed without logging on to Sql server management studio(as you donot have access to SA account or any other windows Account with which you can login)
For this Change below registry key:
For x64 bit
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Microsoft SQL Server\MSSQL10.ARCSERVE_DB\MSSQLServer
For x86 bit
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL10.ARCSERVE_DB\MSSQLServer
Name - Loginmode
Value- 2 for Mixed mode 1 for Windows authentication only
II)Enable SA user Account with new password
-Start the SQL service in Single user mode
-Open Command prompt and enter below command:
-Then enter following commands:
-Restart the SQL service in Multi user mode
-Now you should be able to login to SQL Server management studio with the new password that you entered above.