Yes it should. 64 bit Windows 7 should read all of the GPT disk, even if it is installed on a MBR disk. So there is nothing wrong with the format issue.
If your PC recognized all of this external drive before you reinstalled the OS then something has changed. The question is what? Have you installed all drivers
, particularly the chipset? Did you need to install any software for the external when you got it?
One thing for sure, do not play with the formatting on the external drive unless you have backed up all your data.