I would agree with you that if it was working but has suddenly stopped providing a reasonable issue then it’s most likely a problem with the camera (or associated electrical connections). To start with I’d suggest you make sure the camera cable is plugged in fully at both ends (USB port and the connector in the camera), and also make sure the wires aren’t damaged (especially the crimped ends in the connector for the camera). It may help to try gently wiggling the camera and USB connectors to see if the camera feed sometimes works, in which case it’s very likely there’s an issue with the cable.
I wouldn’t expect it to make much difference, but it wouldn’t hurt to reset the camera and streaming settings by going to the companion web interface Camera page while your computer is connected to your ROV (camera should also be plugged in to the companion computer as usual). Press the ‘Reset to Defaults’ button at the top left of the ‘Camera Settings’ section, and the ‘Default gstreamer options’ button at the bottom left of the ‘Streaming Settings’ section.
If that doesn’t help or if you determine that your cable or camera are faulty then I’d suggest you contact firstname.lastname@example.org and link them to this thread, so you can discuss a potential replacement or refund (or any extra tips they might have for getting it to work again). If you’ve got the order date/order number that would be helpful to include in your email