Can't upload videos to my Facebook Story

While I am able to upload videos to my Facebook News Feed, when I click the button to add a video to a Facebook Story, a directory window opens but the video MP4 files are dimmed out and unelectable. Why is this and what can I do to upload my 5 second video to a create a FB story? When I click the plus sign on the My Story image at the top of my News Feed, I am presented with two boxes. One says "Upload a photo" and the other says "Upload text." Where is the box that says "Upload a video?"