I don't think I've done anything to the build.prop (I didn't even know what it was until I Googled it) and the only thing I can think of that might have effected anything is that I did the "thumbnail .nomedia trick" (that's where, when video thumbnails are taking up too much room in your system, you create a file called ".nomedia" in the thumbnail folder and delete everything else and the thumbnails won't be recreated). Maybe that's connected, like you can't edit videos that don't have thumbnails or something? But the problem was that I couldn't even download the Video Editor in the first place, so I don't know.