When reinstalling OS X I get sent to the Open Firmwear screen??

I have been having troubles with my G4, one day i turned it on and it just went to a blue screen, so i read a few threads about it and how i might go about fixing it and have tried everything. I am now trying to re-install OS X. when I turn it on, i press opt and choose the OS X install dvd, it then takes me to the firmwear screen. I dont knwo what to do from here? can any one help me please?