Sorry to hear about the problems uploading your video Anna and our team is happy to help you get this working!
What kind of error are you getting when attempting the upload? Could you send us the error message so we can take a look at it to see if we can diagnose the issue?
It is possible that your video file does not use an extension that is supported by the standard WordPress configuration, but since the entire platform is open-source there are some ways to work around this. I was able to locate a plugin in the public WordPress repository named WP Extra File Types that adds to the list of allowed file extensions and could help you get the video uploaded.
I look forward to hearing back from you soon Anna!