|First of all, you shouldn't be using the default Administrator account for every day computing. |
That said, try booting to Windows safe mode (F8 at start up). You should be prompted to enter the administrator password at that time. I suggest you copy any personal files stored there to another account.
If you are the only user you can grant administrative privileges to that account, which will then allow you to perform about anything you could do in the default administrator account.