I went to Home page, Live and selected NBC. A password was generated, which I entered on thru my phone on the roku site and it said you are now ready to stream,. 3 dots appeared on the TV blinking in sequence, but no picture
Try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel back once more.
Does this clear up the issue you are seeing? Please keep us posted what you find out.