In cases when there are no provisioned accounts in a SQL Server instance which are known or working, then there is an option instead to run as nt authority \ system (local system). Note that in SQL 2012 local system no longer has sa and you will have to instead start SQL Server in single user mode. http://technet.microsoft.com/en-us/library/dd207004.aspx
This method basically involves creating a new windows service which starts an interactive command prompt.
1. sc create _IC binpath= “cmd /K start” type= interact type= own
[SC] CreateService SUCCESS
WARNING: The service _IC is configured as interactive whose support is being deprecated. The service may not function properly.
2. sc start _IC
[SC] StartService FAILED 1053:
The service did not respond to the start or control request in a timely fashion.
3. Check for the spawned dialog and click view the message
4. This will then lead to a command prompt running as local system. When finished close all your opened apps.
5. The final tidy up step is to delete the elevator sc delete _IC
You need psexec from http://technet.microsoft.com/en-gb/sysinternals/bb897553.aspx
1. psexec –s –i cmd