Make sure you are connected to the correct HDMI (select appropriate HDMI input with your TV remote). Press the Home button on your Roku remote and see if anything happens. If not, unplug your Roku Ultra for a min, plug it back in, and see if it now boots to your screen.
If still no-go, try plugging something else into the HDMI port (gaming device, dvd player, etc) and test to make sure the TV's HDMI port is working.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102