You've gotta get a special cart that you can connect to your PC. Then you can flash ROMs onto it via a USB or other cable and play them on your GBA. Search up an EMS USB Gameboy cartridge and you'll get the idea.
DON'T STEAL GAME ROMS!!! I use this to run Little Sound DJ and make music, not to steal games.
They only cost a couple of bucks now, so just go buy the carts, man.
Unless you need to do this explicitly because you're bumping the cart and causing it to freeze, in which case I cannot help you. Maybe you should check out the newer GBA systems such as the micro? They load from the top, which means you can't bump the games when you try to play them.