Before continuing, take a moment to double-check and make sure the SATA cable is plugged in securely to both the second hard drive and the optical drive connector.

Put the upper case back on!

You'll feel the tabs 'snick' to secure the case once you get it all the way down. If the tabs don't engage, check to make sure nothing is sticking out and blocking the case (you don't want to crush your new hard drive).