New installation won't play video files

[ristretto6]

I've been using XNView for years but just got a new laptop, installed a fresh version, and now nothing happens when I click on my video files. Image files display fine in the preview pane, but nothing happens when I click on a video file--not in the preview pane, nor if I double-click on it to open it regularly. What setting would cause this to happen? I haven't made any changes to the default settings since installation.