CD and DVD drive not detected

I have intel 946 motherboard with 1gb ram and geforce 256mb 7100 turbocharge graphics card and two sta hard disk of 80 and 120 gb. My problem is that i have a cd rom and dvd writer and when both are connected with IDE cable both does not show upp in bios if any one of them is removed it shows the one that is connected.
how can i make both my drives detected