You should check the codecs for the program you use to open media files. The Windows forum on Microsoft or the related prog's community or devpage, if such exists, would be good places to start.
PLEASE BE CAREFUL WHEN DOWNLOADING CODECS OFF THE INTERNET.
If you are not experienced with browsing the internet and can't find out how to tell if a codec downloader is legitimate then please be cautious.
Quicktime player can play .MP4s, so can VLC Media Player.
VLC Media Player is a safe and trusted software application that comes with a TON of codecs already.
If you do download a codec from the internet, please make sure that it is directly from Microsoft (unless you know where else to look, or how to validate it is not a virus).
Start a new topic or ask questions in the open forum.
