> I am unsure why the media player now refuses to play files anymore.Everything is as it was before but it still wont play.
By media player do you mean ThumbsPlus' internal viewer?
Do you still see thumbnails for your videos?
When you right-click on such a thumbnail and pick View, does nothing happen? If so, your system likely has a codec problem (no proper codecs for those particular video types is present and active). This can be solved by (re?)installing the [link=http://www.codecguide.com/download_kl.htm]K-Lite codec pack[/link] or by checking its configuration if you already had it.