"This when I had hundreds of important files saved for my business."
The time to worry about important files is not after something goes wrong. With today's technology, it's very easy to regularly back up important files on to a relatively inexpensive external drive, or even a thumb drive.
Computer hard drives can crash at any time without warning. If you have only one copy of your important files and they're sitting on a hard drive, you are needlesly risking your data and your business.
A great many fixes for computer crashes involve reformatting a drive, which deletes all files. I agree that the tech probably should have told you that the files were going to get wiped. Most repair places have standard language in their contracts that explicity tell you that you may lose everything on the drive.
Going forward, regularly backing up your valuable files will make this a non-issue. If you keep up your current practice, it's just a matter of time before it happens again.