Help getting started with Roku devices, including setup, connecting your device to your TV, linking a Roku device to your account at my.roku.com/link, adding channels, subscribing to services, and more.
I believe the "not supported" message probably comes from your tv, telling you the device you are trying to view is sending its video signal in a format not supported by that tv.
Here's what I think is happening:
During the initial HDMI "handshake" in which the Roku and TV exchange information about capabilities, the Roku is interpreting feedback from the TV as saying the TV supports a resolution (4K maybe) that the TV doesn't actually support. So after the startup when the Roku switches its output to that unsupported resolution, the TV can't display it.
I'd suggest trying the Roku on a different TV if you have one, especially if it has a working Roku. If it comes up okay there, go into Settings > Display type and change the Roku to the actual resolution of the problem set instead of the "auto" setting. When you get to the countdown screen click on the "yes" option. Now move the Roku back to the first set and see if it works.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T
I Have the same problem after a lightning strike took out a power transformer. When power returned I can only get the roku start up then it leads to not supported. I tried reset, power off and on, different tv input jacks. No matter what I get the same result. I was hoping there was some way to get it to work.