harddisk repair cannot install os

Uhm okay, well you 'cannot install OS' if the HDD is bad. You would need a 'working' HDD to install the OS. Since your not telling ANYTHING about this system (What OS? What computer model/make? What happened to the HDD? What HDD repair, no one can 'repair' a HDD, they are either working or broken, etc.) that is the best answer you can get.