Are you sure that the HDD is still functional? A HDD running Vista is old enough to have died.
If you did not make a system repair disk and do not have an installer disk, you will need to either obtain an installer disk from somewhere like EBay or use a boot manager repair product like
THIS ONE. Unfortunately, I am not aware of any free fixes for Vista if you lack the disk mentioned.
I would determine the brand of the drive and run the drive testing software downloaded from the manufacturer site before spending anything though to insure that the disk actually works.