Unused Disk after new Windows 7 Install

Unused Disk after new Windows 7 Install

I have a really big problem.I currently had 2 hard drives, disk0 and
disk1. I bought a Western Digital 1TB hard-disk a while ago and installed
it on Windows 8 and it was placed as my disk 2.
I put all my data from long time ago in it and used it for about 5 months.
It was all fine 10 hours ago when I decided to install Windows 7 (in place
of Windows 8). I formatted disk1 entirely (didn't mess anything with disk0
and disk2) and successfully installed Windows 7.
After the process was done I started Windows 7. The problem is that I
noticed that Windows 7 doesn't seem to be able to deal with disk2 (1TB WD
Hard Disk). Windows 7 can see it in Disk Management but doesn't even
recognize the Free Space and the Used Space (should be 470gb used).
I can't even assign a letter to it, the only option I have is to Delete
it. I tried many others software and they do the same, they partly
recognize the 1TB hard drive, but doesn't seem to able to detect
free-space and used space. They also seem not to be able to do anything
with it but to able to delete it. Also, I noticed it probably is in some
GPT Format.
I'm pretty sure I didn't do anything wrong with this disk in the Windows 7
installation process, and I didn't format it.
The data I have on it is really important and I can't afford to lose it.
While all evidence points to the fact that the data is still there, I
still have a lot of fear that the data is all gone.
What should I do?