You can fix it, but you'd need to get a recovery disk or some type of OS disk. Or check if the model has Win 7 drivers available and install that on it. You can put XP on there also, but you need a disk and a key to install it with anyway, and Win 7 would be a better option. Unless your system does not offer Win 7 drivers.
A suggestion that I always use, buy a second hard-drive to re-install Windows on. That way if the drive is good, you will have all of your old files available.