I have some .mov files that were taken on a JVC Camcorder. When I try to get them into Vegas 15.the audio come through, but the video won't. When I play them in MPC_HC media player it plays correctly, audio and video. I've installed QuickTime as someone suggested, but it didn't help.
Best thing to do is upload a sample clip that can be downloaded for testing. Most likely you need a tool that either rewraps or transcodes your footage into a format that can be easily imported into Vegas.
Was this a 700 series JVC camera? I used to run into this issue if someone recorded in .mov instead of .mp4 format and was able to find a cure by using this software to rewrap the file(s) from .mov to .mxf which Vegas liked. Good luck.