Windows 7: Forgot Administrator Password

I have Windows 7 Home Premium, 32bit. I used System Tools and did a Disk Cleanup. However, when I tried to boot it up after the process, it asked for my Administrator Password. Why we have to have an Administrator User Account, I have no idea--especially when you can't get into it. I don't remember putting a password on for the Administrator Account. I have another User Account that I can get on the computer with, but I have pictures, videos, documents, etc. on the Administrator Account that I now cannot recover. Is there anything I can do, other than reinstalling Windows?

Take look here:
Reset User Account Password - Vista Forums
User Account Password - Change from WinRE
Password Reset : Using System Restore in Windows 7
User Account Password - Change from WinRE
Password Reset
This works for Vista & Win 7.

I have tried these. However, having to log on as a different user, it, of course, asks for my Administrator Password for permission!! Maybe I am doing something wrong.