Roku was working fine. Now when I turn it on , it loads for about 10 seconds through the bouncing letters and then screen goes purple with the mode not supported message. I can't get to settings to try and change anything as it never gets that far. I have shut off and unplugged, replaced HDMI connection. Nothing works.
The purple screen and message are coming from your TV. I don't know how it could have happened, but it sounds like your Roku device is set up for a display mode your TV doesn't support. Try this, once the purple screen comes up, give it another 10 seconds or so and then try the following sequence of remote button presses: press Home a few times followed by Up arrow, Right arrow, Down arrow 3 times, Right arrow, Up arrow, OK.
That should set it to 720p which all TVs should support.
My TV with ROKU was working for several months. As of yesterday, I have the same problem described above.
