There are several possible causes of this issue, including a temporary software/firmware glitch, or a hardware failure.
Initially, please unplug power to the roku box for at least 5 minutes, then replug.
If no change, look on the back of the roku for a small hole labeled reset, press and hold a paperclip or pin in there for about 15 seconds (with power connected). If it is still unresponsive at that point, it would leave only the possibility of a hardware fault. In that case it would need to be replaced, which should be covered under the roku warranty. In that case call(###) ###-####to file a warranty claim and they would send you a new roku.
My apologies for the potentially bad news.
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