Videos as objects - Dragable videos

When I first started using Storyline, I was able to set up triggers using embedded youtube videos as objects. Imagine this:

Spelling drag and drop game. It has four videos on the left and four tiles on the right with the words on them.

I was able drag either the video on top of the tile or vice versa and make them both disappear. Now, I am not able to get the videos to show up in my triggers menu. What do I need to do to make it where I can drag a video?