If you selected a video from your computer
Your browser cannot persist file locations for security reasons. It generates a fake path every time you select a file and that path is only valid for the current session.
If you're using one of our Pro tools you can open a video with Ooona's Agent which will persist the file location.
If you're not using a Pro tool or you just don't want to use the Agent you'll need to either use an online video (by providing a url) or select the local video every time you start working on a project (you can drag & drop it into the browser page to make it faster).
If you've provided a video url
Copy the video url to a new browser tab and make sure it's accessible and playable on your browser.