Setting Default video app (click on link)
Go to LW 's library window, select the folder the video file is in & press the Explore button. Sample image here:
Using Library Explore button to access downld folder (click on link) & the folder will open up for you. Then you can move it or find its location & direct VLC to that location. See if it plays. If VLC cannot play it then I'd suspect the video might have a problem. But you did say more than one video file. What format are they? (avi, mpeg, wmv, etc.)
It may be a system issue with default for video files has become mucked up.