windows 7 admins was changed and user added. cannot log onto old name

Hello everyone!

While I was away, my brother and his friend were on my pc. They added a new windows user and gave it admin privileges and then took away the first accounts admin status. I'm really super pissed but that's beside the point. What they told me is that they made a new account, changed my old users name and made it a standard one. I can see all of my old files from this new accounts login. There's something weird though... I went and restored admin status to my old account and made it visible again by adding it to the groups it used to belong to. Before when I booted up my PC, it wasn't even an option to select it. But now I see it and I can't log onto it. What happens is that I click it, then it says "shutting down" (but it doesn't actually shut down). Then it just takes me back to the user select home screen. I can only log onto the account that my brother made and I can still have access to my old files as long as I click OK if it asks me to open it with admin privileges. Not too sure what to do.

I just tried going to regedit and fixing the names and such on the HKEY_LOCAL_MACHINE -> SOFTWARE -> Microsoft -> Windows NT -> Profilelist. I can't change the name of the user. It says " Cannot edit ProfileImagePath: Error writing the value's new contents". What I tried saving was "C:\Users\(my name)".

and I just wanted to correct my last post. When Im at the user select menu, I click on my old profile and it starts up and immediately goes to "logging off". I'm just super grateful at this point that I can still see all my old documents so far. I still feel so lost though.