take out your harddisk (1)
put it in to ANOTHER PC, but don't boot from harddisk(1), so you will have 2 (or extra) harddisks in one PC.
Boot up the 2nd PC and login, then you will be able to access harddisk(1). Do a backup, then you will be free to reinstall or do whatever to harddisk(1) now...as you will have all your files and stuff in the 2nd PC.