If you know where all the data you really need is I would recommend making a Linux Live CD and through that moving all files that you require (even ones you ge the Admin problem with on Windows) onto an external drive/DVD.
Instructions on how to do so can be found here https://help.ubuntu.com/community/LiveCD#Preparing
your LiveCD (if you can't do it on your PC try and borrow someone elses to do it.
After all your data is backed up, format your drive and re install Windows.
It's not an ideal solution but something is really really wrong with your PC.