How are you powering the device? Is it plugged into the TV USB port, or is it plugged into the wall outlet with the provided cables? In addition, have you tried using another HDMI port on your TV as well as trying your device on another TV to see if you are seeing the same issue?
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It’s plugged into one of two HDMI ports on my tv, the other powers my tv satellite receiver. So I have no spare ports and no other tv to try it on. What puzzles me is why my roku should suddenly stop working after years of use unless it has died. You’d think it would at least have a light when switched on. Thanks for responding, hope you can solve this.
Ignore that question about the USB port. The Roku 3 doesn't use its USB port for power. It's possible your power adapter has died. I think you can find a new one at https://www.roku.com/products/accessories/player , but they don't list the 4200. @Tivoburkee can probably tell you which one works or you can search online for "Roku 3 4200 power adapter" to find a compatible one. Other than trying a friend's Roku 3 power adapter I can't think of a way to easily test the one you have.