Welcome to our Community and thanks so much for your first post - I am sorry that you seem to be having a loss of picture on the TV currently.
Usually when you can hear sound and no pictures, it is a loose or damaged HDMI cable. Have you checked to make sure they're all secure or have you been able to try a new one for us at all?
I have been able to locate your account in order to do some checks from here for you - however, we are not able to connect to your box as it is advising it is currently switched off. If you are still having the issue, please do switch it on for us, ensure it;s not in standby or low power mode and we can go through some more checks with you if needed.