Depending on the model number, your Roku is either 5 or 7 years old. It's possible that something has failed inside. The Roku 3 is still technically supported by Roku, meaning it still receives OS updates. But it might be time to consider a replacement. You might try using a can of compressed air and blow out the SD card slot, in case there's something lodged in it. You also format the card in a computer first (the device will still want to format it in it's own format), just to make sure it's not bad.
Also, there's no requirement to use an SD card in your Roku. It merely increases the channel storage on board the device. But it will work just fine without it.
Dan
Roku Community Streaming Expert
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