hey i own a pm g4 and i recently installed a new dvd drive. the dvd drive is working fine but when i turn on the computer it doesnt go any further than the apple loading screen...whats wrong and is there anyway i can fix it? a few weeks ago a compusa guy did a " apple check " or something and it seemed to make it run real smoothly. what is that and how could i do that? any responses would no doubt help me alot.