What was the result of the Hard Drive test? And the result of the RAM stick test?
This is a very incomplete answer you provided us. If the file failed to play/read on a different computer, then that hard drive has most likely failed and it must be replaced.
You mentioned also that you could not backup files to/from that drive on your Boss's laptop. That's another indication of failure.
If the Hard Drive and RAM tests passed, that drive could still be bad.
You should consider taking it to your local Computer repair shop and having a Data Recovery done on to get whatever you can off of it. This would cost from
$40-$120 US here. If your local Computer Tech can not get anything off of that drive, it will then need to get sent out to very very expensive professional Data Recovery. This can cost upwards of
$550 US. Will your Boss be willing to spend that much to get that media file you are having problems with recovered from that drive to his internal drive on the laptop via DVD or USB? Does he have other files in his Library folders that he also needs back?
You will probably need to ask him if the other stuff he has especially documents and photos are important enough to him that he would be willing to pay for these Data Recovery services. At this point, you've exhausted home testing methods and I wouldn't try to do anything else on that external drive that could further degrade the file structure that's left. You should purchase him a brand new external drive for his laptop, or tell him to buy one (name brand preferably such as WD or Seagate). Then take the broken drive with his files on it to your local repair shop for initial Data Recovery attempts. This can take a few weeks. If they can retrieve anything off that drive they will provide to you on removable storage media and you can copy it back onto his new replacement external drive and he can continue working.
By the way, did your Boss create that media file or did he download it from the web or save it from an E-mail attachment that someone sent to him? What file format was that file? Does he have backup copies of that file somewhere else? If he does, as a test when you get the new external drive hooked up to his laptop, you should copy the backup copy of the media file and make sure he can play/read it from the new external drive. If that works, you've now fixed his problem!
<<<BBJ>>>