Make sure, you select tool, which is appropriate for the brand of your hard drive.
Depending on the program, it'll create bootable floppy, or bootable CD.
If downloaded file is of .iso type, use ImgBurn: http://www.imgburn.com/ to burn .iso file to a CD (select "Write image file to disc" option), and make the CD bootable.
NOTE. If your hard drive is made by Toshiba, unfortunately, you're out of luck, because Toshiba doesn't provide any diagnostic tool.
Thanks to Broni for the instructions