Why can I play the video in my prezi on my computer but not the computer I am using to present?
This could be related to a firewall at your office. We often get emails from teachers and people from certain offices who can use Prezi with no problem at home but have issues at work (e.g. YouTube is often blocked by schools). Unfortunately, there is nothing we can do on our end to solve this - you need to discuss it with your IT department.
If you run into other Prezi-related issues, please let us know.