Check your IDE cable for damage, check the drives to make sure the master and slave are correct, make sure you are using the 80 pin IDE cable instesd of the older 40 pin variety, also make sure the red line on the IDE cable is inserted where the pin 1 is marked on the HD.

I ended up getting a B&W g3 with a g4-450 zif for just shipping because the IDE cable was damaged (underneeath the motherboard out of view) and HDs would not show up.