PowerPoint crashes if I try to modify/open an embedded video file

I hope someone can help with this! I have a new Dell laptop and Office 365 installed. I am trying to get a presentation ready for this week...I am able to embed a video clip into the powerpoint presentation, however when I open the presentation if I click on the slide containing the video clip is closes powerpoint altogether! So I cannot edit the size or position of the video.

Any ideas? Many thanks Sarah