Lost Password/Locked out of computer

We are trying to help a friend fix his computer. I use XP, but his computer
is Vista Home Premium, so i don't know anything about Vista.

The problem is when he signs on, he is prompted to enter a password. He does
not have a password assigned. He also has no access to any other account
choices...only his. I used Trinity Rescue Kit, and it says no Windows
installed. I tried Ophcrack, and the passwords are empty for his account,
administrator, and guest. Vista cd's did not come with the computer. Is there
any way to repair this without having to restore default settings? Will
everything be lost if restoring default settings such as pictures, etc?

Thanks for any help you can provide.