There are a lot of failure points with a Fakebuino, I would recommend doing it one step at a time:
1) Upload the blink sketch with an FTDI cable and ensure it's working (there's a D13 LED on the board).
2) Connect the LCD and make sure you can run the sketches at
http://playground.arduino.cc/Code/PCD85443) Change the LCD pins to what the Gamebuino uses(see the Wiki), make sure the LCD still works.
4) Connect the SD card using the same pins as Gamebuino, make sure the library SD examples all work as expected.
5) Format your SD card with FAT16 and hook up the buttons. Now press C while powering up, this should cause the loader app to be launched from the SD card.
6) If you have a ProMini with the extra 4 analog lines exposed then tie A6 high so that games don't give you a low battery warning, and tie A7 (ambient light detector) either high or low, depending on whether you want the backlight to be on. (If these aren't exposed on your board then you'll need to recompile games with a modified library to disable the battery check).
7) If you want sound then grab a 1k resistor, a general purpose diode and a general purpose NPN transistor and hook up a speaker to D3 as shown in the gamebuino hardware schematic.