new to mac's

i bought 2 imac g5's , power mac g5 when turn on imacs hear bwoooo sound , goes grey screen. have apple keyboard possible first imac or g3 clear usb ports on top have tried boot cd's have burned no luck...i insert cd hold down c , grey screen question mark folder. turned off computer installation media still in held down c , restarted still went grey screen have windows based machines. there anyway tell if installation media correct , working? there way boot? know can cheap version of tiger or leopard 10.5? looked serials , have found these power pc based can me , not advice of buy new mac lol

 

i opened installation media transmac , showed me bunch of folders right?

 

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