I opened case of HP a250e. Free slot behind existing drive appears larger than slot (bay) for existing drive? I find no instructions in manual or online as to how to remove the bay and install 2nd drive. Why would empty bay be larger? Maxtor drive came with desktop, and wish to install a Wester Digital 80gig, which appears to be of same size as the Maxtor, wo what gives with the open bay size looking different?