I work for JVC and would like to try to help.
If it's a Windows computer, always make sure you install the CD-ROM that comes with the camcorder, even if you do not plan to use the editing program or player program it comes with. That CD-ROM should give your computer all the necessary video and audio codecs that are needed for playback.
If that does not work, please post with the exact model of JVC camcorder, as well as the type of computer and the version of the OS that you are using, as well as the player program that you would like to use.