If the screen is completely blank as a black color (from what it seems like), it is very likely you have a damaged panel or ribbon cable on the LCD.
If it's not those, your motherboard may be faulty (considering these GBAs are about 20 years old) so you either might want to look into replacing the LCD (especially if you want to install an IPS mod kit for a backlit, clear picture) or to replace the motherboard or console if the problem persists.