dp leopard g5 will not boot from super drive or allow return

trying to boot from supe rdrive..will not boot....and will not allow return to hard drive...have used all the key-stroke comb's I can think of....have zapped pram...have used reset button....when super drive comes up monitor displays lock on left of screen bar to its right and arrow pointing to rt.....then text asks for password which is obviously different from my own password........any suggestions before I heave this thing out the window????

UPON DEPRESSING OPTION KEY-------WHITE SCREEN APPEARS W/LOCK ON LEFT---BAR IN CENTER---ARROW IN RECTANGLE ON RT'(POINTING RT). IF I DEPRESS KEYBOARD ARROWS' SCREEN GOES TO TEXT....ASKS IF I WISH TO CONTINUE BOOTING OR CANCEL....'WHEN I ENTER EITHER WAY....TEXT ASKS FOR PASSWORD....WHICH I DO NOT HAVE....