The answer is that you most probably have a hardware problem. First, before you do anything else, if you haven’t already, I would recommend you back up anything important on that drive. I know you say the drive tested fine but there is some reason why your computer is having trouble booting to it.
2. Remove everything but the CD/DVD drive and Hard Drive from the boot sequence (on this laptops Bios highlight the device and press x to remove it from the boot order, but it could be different on your computer)
3. Save and Exit the systems BIOS - Very important that you Save the settings before you exit.