Do your .m4v files have DRM? I have heard of people not being able to play them, or only getting sound with no video, if the file has DRM. If you downloaded them from something such as iTunes they probably contain DRM. I can't say that I recall reading about anyone not even seeing the files in their library due to this, but I don't know for sure on that. If you can see the files in files mode, be sure they play ok through files mode. If not, maybe that is your issue (maybe not, but if they don't play properly then it's a moot point anyway
)
Assuming that your files play fine, and there is no DRM...
These are all pretty obvious questions/suggestions but often times those are the things you tend to take for granted and overlook.
When you set up the source did you set the content type (TV Shows) and scraper (TVDB)? Double check and re-scrape.
Have you tried simply deleting the source and adding it again?
Are you importing a library from another copy/version of XBMC?
Do you have "Hide Watched" enabled in your skins view settings?
Do you have nfo files for all of your shows?
If not, that could help (though XBMC should still be able to scrape the majority of them with the TVDB scraper even without the nfo files...).
If so, did you create them yourself, have a 3rd party app create them, OR were they created by XBMC?
When you added the source, did you select "exclude path from library updates"?
If all else fails, as X said, enable debugging, scan for new content, and post a pastebin of your log.
