Not recognizing internal HDD on 2007 model macbook.

So I've installed a WD 500gb as a secondary drive in my macbook '07 model, and if the macbooks keyboard is unplugged then it recognizes the HDD. As soon as I boot it up with the keyboard plugged in it no longer sees it. Is it some kind of power issue? It's like the logic board can only deal with one or the other.