The very FIRST thing you do is take you hard drive to a professional and get him/her to back up your data to some other media type: USB drive or DVD.
Then explore options for fixing your computer.
Please listen to clee1. You do not have a computer problem. You have a data problem. The computer is not important.
Take the hard drive to a friend with experience in the matter and have him or her recover the data. This is often no more difficult than mounting it and searching the drive for files in Documents and in other folders that you already know about. THEN you can worry about the hardware and OS.