Hold the button on the TV keypad and plug in the power cord.
You have installed firmware for the wrong resolution. Find the correct .bin file specific to your panel model.
Try a different USB drive (4GB or 8GB is best). Ensure it is in FAT32 format.
If you are unable to find the correct firmware, or if a firmware update fails to resolve your problem, the next most practical solution is to replace the mainboard entirely.
Downloading the wrong firmware will "brick" the board (black screen, no power). You must match the Panel Resolution and Keypad layout to your specific TV.