you need to find out, what the corresponding key on your cab is. open "notepad" and press the buttons and joysticks to see, when "5" appears on the notepad. remember the button or joystick direction you pressed and try it then with the screensaver attract mode of GameEx. also you maybe need to compile MAME for "direct input". try "CabMAME" or "GroovyMAME" for your Cab. they are the best MAME versions for people, who have a MAME-Cab. I HIGHLY recommend them . they have optimized resolutions and solutions for CAB-usage, including HiScore Save and so on.