Do you have a Windows 7 DVD to use as a repair disk or can you download the necessary files from Microsoft and make a bootable disk? The problem is easily solved when you can access the Administrator account.
Have you tried Safe Mode with Command Prompt? If you can, at the Prompt type
net user Administrator active:yes
then hit the Enter key.
Restart the machine and go to Safe Mode then click on the Administrator's logo instead of your own. If you get that far, post back and I'll try to track down the psot I put in here somewhere as to what to do next.