I'm currently running Win 7 Prof. I have the 3tb to 746gb issue. The thing is, I've always been able to use this 3tb drive until recently. This 3tb drive is my video streaming driver. I have thousands of avi. files on it.
I recently tried attaching the usb port up to my wireless router network port. This was not working as I would like, so I plugged it back into the computer to use the normal way of just sharing the drive.
I found that there was a problem when I simply went to play a video on the computer, windows would not read. Taking a look in the folder, all my files are there, but now there are files that shows 0 for size. There are a bunch of files that has a size 0. I'm assuming this is from the 3tb to 746gb issue.
In disk management, the top portion shows the incorrect size, but the bottom portion shows the correct size. I have 2 other 3tb drives that shows correctly attached. This is the only drive having issues.
I hope what has to be done doesn't delete my data.
What's happened to OP is that he's moved the drive to a controller that doesn't support 64-bit LBA, and accesses to the drive are "wrapping round" like what used to happen with 137GB drives in controllers/OS that didn't support 48-bit LBA.
Attempting to write to a drive that appears to have a smaller capacity than its true capacity will certainly result in filesystem corruption: the OS will write data to what looks like the correct place, but the controller will store it in the wrong place, over the top of existing data.
This is what has happened to OP's drive: he plugged it into a computer that didn't understand drives that size, wrote to it a bit, and corrupted the filesystem.
The drive itself is fine: hard disks do not announce their imminent demise by shrinking in capacity, they do it by making horrible crunchy noises and presenting a normal-looking filesystem that can't be read. His data's probably toast, though.