Only User is a Standard User

Hi,

Windows 7 Pro

When I set up this new computer I created the main account as a standard user. Bad move. Now whenever I try to make any changes I get the UAC prompt with a disabled "Yes" button. It says to enter an administrator password - there isn't one that I'm aware of. I'm not able to use the cmd as administrator either. Am I going to have to reinstall Windows to fix this? I've tried several suggestions I've found on the web (safe mode, etc...) and nothing is getting by the UAC.

Thanks!