How to adjust the backlight of my gameboy agb-001

Problem

the screen seems so dark

Solution

1. That particular model does not have a backlit screen. The original Gameboy advanced models like yours all had no backlights and this was a major flaw in the systems design.
   
   There was a company that made something called the afterburner. This was a backlight system that you could add to the gameboy, but it was pretty tough to install correctly as you had to take the entire system apart and could damage things.
   
   Your best bet would be to trade in your current model at a gamestop or similar store and try to pick up a Gameboy Advanced SP model (the square one).
   
   The Gameboy Advanced SP was a redesign of the original GBA and featured different dimensions, and a larger / backlit screen.
2. I have the same problem...I've heard that it's the battery in the game cartridge that has gone dry....People have said to go to a jeweler to get a tiny battery to replace it, but youll have to open up the cartridge...