I generally view films by going directly into my "films" folder. I select a film and double-click it or right-click/open it.
I never actually open the filmviewer myself, it opens as the film opens. Try it that way.
Once the viewer opens, I just click the play button.
A couple of "hints"-
You need to adjust your head position inside the viewer, for best results. You do this just like in the game, by using the arrow keys and Page Up/Page Dn, and then saving that view with F10 (the number-pad allows you to "look around" i.e. the number 4 looks left, and number 5 looks up...). Personally, I set these views, and then re-start the film and watch it "properly". Now, these views will save "forever", but will be "wrong" if you view a film from a sortie using a different plane-type. In other words, if you set the views for a spitfire, they'll be "wrong" for a 109. You'll get some odd perspectives, looking at the headrest, etc... You need to re-set the views for each plane-type, and when you do that, they're not going to work for the original plane-type anymore. In teh game, the various view-sets are saved for each plane... It's not as simple in the viewer...
Speaking of views, over on the right-hand side of the viewer screen, I'd recommend checking the icons, trails, and "use saved views" options. This gives you quite a bit more information, including where you were looking, and when...
At the top of the screen, there's a slider that defaults to 1x. That's play speed. I slide it up to 2x for boring parts of the film, and return it to 1x (or slower) for other parts.
You can also edit films using the viewer. So, if you film a 45 minute sortie, but only want to save a 5 minute segment, you can do that. You can also remove text, voices, etc...