I assume you have an eSATA external connection? How many SATA controllers do you have on your system?
Something you might try is to open device manager and click on the little computer to get Windows to look for devices. It should find and install and external drive, if it was not plugged in during boot.
To make an eSATA drive behave like a USB and be hot swappable, you probably need to set up your SATA controller the drive uses for AHCI. On my system, I have the primary SATA controller set to IDE and the eSATA controller set as AHCI.
The last time I had any experience with an external rack or multiple drive situation it seems the software for the rack was supposed to handle the communications with the computer. Since I do not run one, I cannot give you guidance about how to set that up or what might be wrong. Knowing the exact device, may help.