How do you know this exactly?two completely fine hard drives
Use something else to boot the computer. Is this Windows 10? Can make a Win 10 Install USB / DVD with the Media Creation Tool here:
You will need to run this on a working Windows computer and you will need an 8GB or larger USB flash drive, or a blank dual layer DVD and DVD burner.
Boot the problem computer with the USB/DVD, choose Repair Install, and you should be able to get to the advanced settings. Where you go from there depends on what the problem is.