If that fails, the file is truly bad or just so oddly encoded that it's dead Jim.
Am using WMP on Windows 7.
A Mac user 'emailed' me a one-hour .mp4 video file, via WeTransfer, a cloud-based file transfer service.
I successfully download the file, click to play and it opens but then it is blank. Properties show it is an mp4 and that his has 647 MB of video lasting 59.34 minutes. On opening, the timelines also shows 59.34 minutes, and it 'plays' through from start to finish but there is no sound or video.
TIA for any solutions