I would make sure the little USB power adapter is the right one since all of those little blocks look the same. See if it has "Roku" on it somewhere or look at the fine print and make sure it says something like "Output: 5V 1A" (or 1000mA). If that all checks out then the next thing is probably a factory reset (usually the last resort). With the power connected use a paperclip or something similar to press and hold the reset button for no less than 30 seconds while ignoring anything that may appear onscreen.
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