1. Use the supplied power adapter rather than the TV USB power port.
2. Try using another power adapter and/or power cable. (cell phone USB charging adapter 5volt, 1amp, cell phone charging cable with micro USB on device end)
3. Plug directly into wall, eliminate surge protectors/power strips for testing.
4. Restart Roku device. (unplug unit for a min or so).
5. Factory Reset your device. (press and hold Reset button or pinhole reset for 30+ seconds)
6. If still no go, device replacement likely needed. If under one (1) year, then should qualify for warranty replacement. (https://support.roku.com/search/warranty)
Otherwise you can review Roku Support troubleshooting for device issues here. (https://support.roku.com/category/4403790058903)
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941