“When I try to play m2ts files they cannot open and I have to right-click, browse for a program, and select Windows Media Player. When I do this the m2ts file plays only the video portion but not the audio portion. I have two questions:
Q1) What causes the m2ts file to not open?
Q2) What causes m2ts file to play only the video and not the audio?”

The m2ts file format created by recording video with AVCHD camcorders is not recognized by Windows Media Player as a playable file format. It combines h.264 video with AC3 audio in an MPEG-2 transport stream, which generally confuses most media players. Each of those components are playable in Windows Media Player, but not in that configuration. h.264 is typically played in Windows Media Player as either an AVI or MP4 file when the proper codecs are installed. AC3 audio is associated with many different video formats, but also requires its own special codec for playback. In general, MPEG-2 transport stream files played by Windows Media Player are only found on DVDs. For all these reasons, Windows Media Player does not recognize the m2ts file as valid, so it won’t automatically play the file. In many cases, Windows Media Player won’t play m2ts files at all.
In answer to your second question about why the video plays but the audio won’t, you are most likely missing an appropriate audio decoder for playing back the audio portion of your m2ts file. For some files this can be solved by simply installing AC3Filter. For m2ts files, this doesn’t always work because of the non-standard configuration of including the h.264 video and AC3 audio in an MPEG-2 transport stream.
To reliably play back m2ts files on your computer, your best bet is to purchase software that supports the m2ts format properly. The solution I prefer for this is PowerDVD. By installing PowerDVD, you typically get the option of playing your m2ts files either in the PowerDVD application interface or playing them in Windows Media Player. Download PowerDVD to playback m2ts files reliably on your computer.