I am powering the 4800-X with the 12V 1.5A wall power supply.
@cshen, try another input on the TV, another HDMI cable, or another TV entirely. If none of those help. find the reset button on the bottom and with the power connected press and hold the button for no less than 30 seconds regardless of what's happening onscreen.
I’m having the same issue, I have tried everything and I’m not able to get passed the jumping ROKU letters. It worked find 2 days ago, but today won’t work and I can’t even reset it.
Roku Ultra 4800x. Worked fine a week ago. I hold down ‘reset’ button for 30 seconds and it starts with dancing ROKU letters. Then just goes blank. Same thing on 3 different tv’s. Please help.