You can try to reconnect the HDD and see what happens, but it usually doesn't work out. And realistically, there is no way to load an OS without deleting everything else on the HDD. You can try the "upgrade" or "repair"/"reload"/"reset" option before a clean install (where the loader will try to save all the 'personal' files while only resetting the OS), but again, that often doesn't work out, either.
In my world, I skip the whole try this, try that, and go straight to the "wipe the HDD and do a clean install" part. Of course, I have really, really good backups of everything, too, which helps.