Check the jumpers on the slave drive, to make sure they are correct, and also make sure you have connected the IDE cable correctly, to the right terminal on the cable.
Does the drive show in the list when you boot up?
Have you had a look in your BIOS to make sure it's being detected?
Lastly, how big is the new hard drive, and how old is your PC? Some BIOS's need to be updated before they will accept large hard drives, but don't go there before speaking to an expert.