Sometimes, being an Administrator just isn't enough. In that case, try being the SYSTEM account... You can run processes as the local SYSTEM account quite easily with PsExec (64-bit).
Use it as follows:
psexec -i -s cmd.exe
The command above would run a command prompt as the SYSTEM account. You can replace cmd.exe with something else, although from a command prompt, you can basically run anything else, all as the SYSTEM account.
Use with caution
Running processes as the SYSTEM account can be potentially dangerous as you will bypass several built-in security restrictions. But I guess that's the reason why you want to use the SYSTEM account...