Installing a CD Rom

I’m installing a CD-Rom on an old machine… the pc didn’t have a gray data cable long enough to hook the cd-rom into it as well as the hard drive. So i got a new cable, and hooked the hard drive into the cable it works, when i also hook the cd-rom into it, it gives me a error on boot up saying that there is NO operating system installed.

some related info: There is power going into the cd rom… the machine works fine if i take the data cable out of the cd rom but when i try to boot up with both the hard drive and the cd – rom it gives me the error. any help @ all would be appreciated – thank you