@alice06
The power adapter (power cube) has to be rated for 5 volts, and at least 1 amp.
If you are sure your new power adapter meets those specs and are still having an issue, you may just have a failed/failing device.
If less than 30 days old, you should qualify for a refund under warranty. If older than 30 days, but less than 1 year old, you should qualify for a replacement under warranty.
Step-by-step instructions for returns and warranty replacements - https://support.roku.com/article/208757058
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