We bought good quality HDMI cable & ended up claiming a warranty on our Roku ultra for doing the same thing. The 1st day we installed the new on sent from Roku it did the very same thing. Any ideas what to try?
While there could be other things, these would be most likely.
You indicated, but didn't specifically say, that you changed HDMI cables. Yes, you said you bought some new ones, but you never said you first tried others. I'm going to assume you did, but if you only ever used the one set, then you need to try another cable and test this.
You changed out the Roku device. Yes, it's possible for two to be bad, but not likely.
That leaves the TV HDMI port. Most TVs have multiple HDMI ports. Try another one.
Also, if you have a device connected to one of the other HDMI ports, power down, unplug the HDMI cable from the other device and plug it into the Roku, then power up and see what happens.
DBDukes Roku Community Streaming Expert Note: I am not a Roku employee.
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Another solution would be to disable the auto power savings under system > power > auto power savings.
I also found that I can wake up The Roku by using the Roku app. The on screen display will say no signal but from the app if I select a channel (YouTube for example) the TV responds as you would expect and everything comes back to life. If you have a remote with channel shortcuts, pressing any one of the shortcuts should also bring your Roku back to life.