play mp4 on computerHow do I get an MP4 video to play with sound intact?

My laptop works fine with all of my videos from other sources, WAV, AVI, MP3, etc. The only problem is that my cell phone records video in MP4 format. I downloaded a codec to play MP4, and my computeplay mp4 on computerr plays the video portion fine, but there is never any sound. Also, if I convert the file on the internet, the sound is deleted. Is there any way to get the video and the sound both on my computerplay mp4 on computer?? Thanks!!
When you install gomplayer, you can play your mp4, .avi,.mp3 etc
Gomplayer is free and can play anything.
Go to preferences -- others -- select all
file types -- codec