The Mac automatically detects whether there is a display attached via VGA or not, no need to fool around with Fcn+F4 (my old Vaio had that same exact key combination too).
Your best bet is to connect an external monitor to the iBook. IIRC they require a converter cable from iBook-->VGA (the port on your iBook is a squarish looking thing), hopefully you got one with it. If the external monitor works, then your display probably has a loose connection. If it doesn't, you may have a bad video card (more unlikely as it was working fine before, but a possibility.)
The Apple logo on the back works by the backlight of the display, so if the front of the display won't light up, it won't either.