I have a Now Stick, with current firmware. It works happily on one TV in the house. I have just tried to connect it to the TV that I used with my Now White Box and i currently connected to a Roku 4200 box which has worked fine for many years. The TV is a Toshiba 42hl57-42 - details here https://www.cnet.com/products/toshiba-42hl57-42-lcd-tv-hd/
When I power up the Now Stick I get the blue NowTV logo, a spinning circle for 5-10 seconds, and then the TV goes black.
I have done a reset, and plugged the stick into the other TV and I see it is in the language setup stage. When I plug it into the Toshiba TV and press the back button on the remote I hear a 'burp' noise which I usually hear when at the Main menu and try to go back.
Has anyone had this issue? Any help would be gratefully received. The Euros are starting soon! 😉
When you say that you have done a reset, do you mean that you have done a factory reset to the stick itself?
What I would try is on the television that the Stick is currently working on, go into the Stick menu Settings and under Display select 720p.
Then swap the Stick onto the Toshiba television.
If that doesn't work go into the Toshiba menu Settings and see if it has an option for CEC HDMI (Regza Link) and switch it off to see if that makes any difference.
Also should you be using an external HDMI switcher box then bypass it and plug the Stick directly into the HDMI port on the television.
If the Toshiba television has more than one HDMI port, then try them all.
According to the link you posted the Toshiba spec says 720p.
Also see if there is a Regza link HDMI CEC setting in the Toshiba menu that you can switched off to see if that forces a picture on the television screen when using the NOW Stick.