GPT Loader created 3TB partition, but now 3TB partition seems undone

I installed GPT Loaded on Windows XP SP3 system with a 3TB SATA drive. I used GPT Loader to successfully create a 3TB partition. I successfully copied at least a 1TB of data to the new 3TB partition. I was able to reboot and the new 3TB partition still existed. All was well.

I had some other hard drives from which I wanted to copy files onto the 3TB partition, so I shut down the computer, swapped a hard disk to be copied for an existing SATA disk, rebooted, and I could not see the 3TB partition. In Microsoft Disk Management the 3TB drive appeared as a 746GB unformatted drive. I swapped hard drives back to the original working configuration, but the 3TB partition did not reappear.

I would like to be able to get back to my 3TB partition without losing the data I already copied onto it.

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Additional information that may be significant: My "My Documents" folder was on the hard drive I removed and swapped for another disk I wanted to copy from. My other user specific folders, such as Application Data, Desktop, Local Settings, etc. are on the system disk.

Originally, when I went to install GPT Loader, I had disconnected all other hard drives except for the system disk and the 3TB hard drive, just for extra safety of data on my existing disks. In this configuration, my "My Documents" folder did was mapped to a disk that did not exist. I could not install GPT Loader because it gave an error in initializing the GPT Disk Manager saying that the D: drive did not exist. When I reconnected the D: hard disk with my "My Documents" folder, the GPT Disk Manager would run and I was able to successfully create the 3TB partition.

My old but useful motherboard only has 2 SATA connectors, and one of the SATA connectors was used for the new 3TB drive, and the other SATA connector was used for the D: drive with my "MY Documents" folder. I can only copy from an old SATA disk if I disconnect my D: drive with the "My Documents" folder, and replace it with my old drive to copy files from.

Could it be possible that not having a valid "My Documents" folder for one of the reboots is the cause of the problem?
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In the GPT Disk Manager, the "Convert Disk to GPT Wizard" shows the following disk list: