You can install the hard drive as a second drive on a functional computer.
You can recover your files and back them up, using a second computer.
You then reformat the drive entirely, or bulk erase the drive.
Reload the operating system from scratch and replace your backed up files.
OR have a computer shop do it for you...about $200.
After that, DO NOT load any more "free" programs into your computer, which is what I am thinking your KIDS did to you. They probably loaded "free" games, or "free" music, or other garbage, which corrupted your drive.