Am I missing something? (eSATA)

I finally decided to try using an eSATA drive, and I'm having an issue. It is a 1 TB drive in a NexStar drive carrier. It works perfectly fine when connected by USB, but when I try connecting it by eSATA, the drive is detected properly in Device Manager, but it won't get a drive letter. When I go into Disk Management, it shows as needing to be initialized. That step always fails. I swapped cables, and even tried leaving the drive connected and rebooting. I'm going to try it on a laptop next, but is there a step I'm missing, or a driver needed for eSATA operation? The system in question is in my Specs, and I have the ports set to AHCI, with the chipset drivers loaded.

Both of those steps suggest a drive that's new or unformatted. This drive is already formatted, and half full of data. It works perfectly fine when connected by USB.

As an update, it worked just fine connected by eSATA to my laptop. At least I know now the problem is with the tower, and not the drive.

I'm going to try another free port on the board today. I know it is connected to an SATA port internally, as Device Manager does detect the drive properly. I have also tried connecting it, powering the drive on and rebooting so it can be detected during the boot process.