|Did you just install this hard drive? Is it a second hard drive?|
You probably don't have the cables and/or jumpers set correctly. It would be easier to help if you describe how you currently have your drives (hard & CD) setup.
One thing I can mention is that WD IDE hard drives have three jumper settings. Master, master alone and cable select (CS). If the 80GB is on a cable by itself you need to use the Master alone setting.
Below is a link to the specs for your computer.