https://support.roku.com/en-ca/article/217787747
Not very helpful article, but generally the three things suggested for this(especially if not seeing red light), is to plug your unit into the wall and do a factory restart of your device. If it wasn't previously plugged into the wall, may just do a System Restart before the Factory Reset. The third is to replace the power supply cable and the power supply adapter.
Sometimes, just unplugging for a bit will solve the problem.
