Make sure that in the Loader Settings, Gamecube Mode is set to Nintendont, also go to Custom Paths and check that the Nintendont Loader Path is set to sd:/apps/Nintendont/ (have my games on an SD card, maybe it looks different if you use a usb). Last but not least, check that in the games folder you have folders for your games that say, for example: Mario Kart - Double Dash!! [Game ID goes here], and make sure that the game files are in ISO format and the name must be game.iso. I had the same problem that you have, USB Loader GX recognized the games but all I could see were black screens. Creating folders inside the games folder and making sure that the game files inside them had the name “game” is what fixed it. Hope this can help you.