Hi Jack. Are your cameras fully installed and fixed in place or are you able to access them easily?
If you can, try connecting a different Cat 5 or Cat 6 lead to see if that makes any difference. On your screen the grey boxes shouldn’t be present if there’s a signal.
It looks as if your cameras are setup via the second stream not main. Right click on the 2 which is at the right of each camera icon, you should be able to switch to the main stream then. Sorry but I can’t remember much more as once I set mine up I hid my NVR away in case we are burgled. It isn’t easily accessible now, sorry.
Try contacting one of the admin on here directly as I’m sure they’ll be able to resolve this for you if the above doesn’t work. Sorry but I’m mostly self taught so not much use.