DIAGNOSIS The stick is receiving power, but the HDMI handshake with your TV is failing. This is common with HDCP 2.2/HDMI 2.1 compatibility or a loose connection.
FIX Follow this sequence. Step 1: Power cycle everything. Unplug the Fire Stick and your TV from wall power for two minutes. Step 2: Re-seat connections. Plug the stick directly into the TV's HDMI port, not through an adapter or receiver. Ensure the USB power cable is fully seated in the stick and the power adapter. Step 3: Try a different HDMI port on your TV, preferably a non-ARC port. Step 4: On your TV remote, manually select the correct HDMI input source.
IF THAT DIDN'T WORK Your TV may require a specific HDMI mode. Enter your TV's settings menu and find the HDMI settings for the port you're using. Disable 'HDMI-CEC' (also called Anynet+, Simplink, or Bravia Sync) for that port. If an option exists, change the HDMI version from 'Auto' to 'HDMI 2.0' or 'Standard'.
HEADS UP Using the TV's USB port for power often causes this. Always use the included Amazon power adapter plugged into a wall outlet. Insufficient power causes boot failures and instability.