You've installed the SSD in your mini, and the prior HD is sitting outside the mini, correct? You'll either need an external case for the 2.5" hard drive or a USB/SATA adapter cable (amazon and others carry them). If you will be using the HD as a backup drive, an external case is a good choice. I like those that OWC sells as many of them use Oxford chipsets, which work well with macs. They even have one that looks like the mini so you can stack one on the other.