When you see previous installations, are you typing "R"? for repair?
If you do not have any option to repair, take the drive out and install it as a second drive on a working XP computer.
Recover all your personal files and make a backup to DVD, CD, thumb drive, etc...
Then replace the drive into the non working computer, reformat the drive, reinstall you OS, your backed up files.
If nothing else is working, that usually does.