Hi Ralph
Thanks for the additional info.I'm not certain what operating system you are on. I'm a PC and a big ole Mac ignoramous. So I'm not sure if Mac will behave as PC (Windows) does.
IF you are using a PC, what does it show when you right-click one of the videos and examine the properties? I'll post a screen capture of my own properties dialog for a .MPG file type.
See the button labeled Change? Click that and you are able to choose any other application that you want for playing the video.
Sorry, but I'm not thinking any of the applications you listed should have caused a change to the file association. Obviously SOMETHING changed it, but I'd be hard pressed to say what.
Hopefully something here will help or possibly someone else will have a different idea of what to try.
Cheers... Rick 