First, try to rule out a power supply issue.
1. If using TV USB power port, try using the included power adapter at a wall outlet instead.
2. If currently using the power adapter at the outlet, try using another power adapter, (any 5volt, 1amp cell phone charger USB adapter will work). Can also try another micro USB power cable, but normally adapter over cable would be likely culprit.
3. If under a year, then should qualify for warranty replacement. (https://support.roku.com/article/208757058)
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102