.MSWMM file

That's not a video/movie. That's the *project* file for Windows Movie Maker. It could be from version 6.0 or earlier.

A project file is like the "save state" of your project. It lists all the source files (just by name and location) along with all the edits you wanted applied. It can't be played standalone as a movie because it isn't a movie. It doesn't have any actual audio or video within it.

If you happen to have all the corresponding source files (music, video, photos, etc.) and they are in their original locations, then you might be able to open that project file in Windows Movie Maker 6.0.

You certainly won't be able to open it in any video program (media player, VLC, etc.) for the reasons mentioned before. And the program you mentioned (Movie Maker Pro) isn't even a program made by Microsoft. It's someone trying to use a similar name to Windows Movie Maker to make you think it is related and to possible pay them money.

Do you know if you perhaps saved it as an actual movie? When you "publish" your project, it creates a playable .wmv (or .mp4) file that can be played in media player. Search for other files with the same name as the project and maybe you'll find the movie already created.