I have the same problem (black screen) now with the 2nd TVIP V.412.
I restart the device but no screen will be showed. is it possible that 2 of my devices are broken in about the same time of use? (max. 2 years old!) or is there any known issue with some firmwares?
First you have to create a new line. After that, click on the Clients Button, where you can see your Costumer Lines. Under MAC Adress, you can klick at "add MAG".