Roku 3 4200x Ultra was given to me by a friend who took very good care of it. I know it's old but when I set it up 4 weeks ago it updated as expected to recent Roku OS (version 10.5.0 build 4208).
It worked fine for a few weeks then failed about 48 hours ago. I noticed that when I switched from using the TV OS to the Roku device, the screen would be blank. Here's what has occurred since then.
1. I did soft reset 2-3x by powering the Roku down, waiting 30 seconds, then powering back up. TV screen still blank.
2. I plugged Roku into HDMI 2 (had been in HDMI 1) port. TV settings show a Roku connected on port 2, but when I switch input to port 2, TV screen still blank.
3. I have done about 3-4 hard resets using pinhole reset button: hold button down for 20 seconds while device is plugged in.
4. I noted one new symptom after the hard resets: now the Roku status light has assumed a new pattern.
The new status light pattern seems to be permanent (did not change overnight). The pattern is: dark for about 2 seconds then 2 rapid blinks on/off. This 2-second pattern repeats endlessly.
(TV is Hisense U6G Android TV which I bought new 7 weeks ago. Android TV OS updated after installation.)
Roku model 4200 is a Roku 3, released in 2013. Ultras are different models, all released since then.
In your 3rd item: Roku terms your "hard reset" a "Factory reset". I don't know if it will help, but to initiate a Factory reset you must hold the reset button in at least 30 seconds.
Thanks, I'll bear that 30-second hold in mind for the next time.
(And thanks for the correction on the model type. The device is marked "4200" on the bottom. I guess the box labelled "Ultra" that it came in from my friend is from her new Roku device.)
Same issue with the constant blinking. Nothing on the screen. Everything I've tried hasn't worked. Still just constant 2 blinks over and over.