" I had is lost.I read that all they do is check what caused the hard drive to fail and everything is then erased. "
they then evaluate what is wrong with the drive, if it is economic, they repair them and ship them off to those who claim warranty on the original hard drives. So in effect you could have someone's old repaired hard drive.
Either burn it to DVD disks, buy an external hard drive or an internal hard drive. On the last two clone the operating system and all the data over. The hard disk manufacturers website should have free software to do this.