Hello there @Harry, I'd be happy to help look into this with you.
It sounds like the videos are either not uploaded to your account or the desktop app isn't syncing.
Could you have a look and see if you can find the videos through the website?
Also, check if you can find the Dropbox icon next to your computer's clock, on your system tray (Windows) or menu bar (Mac).
Give me a nudge with any updates, thanks!