Turn it off by unplugging the device for 30 seconds or by having and checking power cables, switching outlets (if available), or pressing the power button (7-second power reset).
First, unplug it from the wall for like 30 seconds, then plug it back in and try again — that actually works a lot of times. If not, try a different power outlet or cable. Also, hold the power button for 10 seconds to force it into safe mode. Still no luck? Could be the power supply or hardware issue. Might need a repair if nothing else works.
