Local Disk G:...HELP!!!!!!!!

Hello,
I know I might be a tad late, and I'm not sure if this is the same problem everyone else was/is having with their hard drives, but I've been using my 2tb Toshiba portable hard drive for about 5 or 6 months now with no problems...up till last night...
My primary desktop is Win8.1 and that's the one I usually have my hard drive hooked up to. Last night I had some things to get off my secondary desktop running Win7, so I took my hard drive out of my 8.1 (notice I said "took my hard drive out"...no lectures please...) and plugged it into my 7...only to find that instead of the name of my drive coming up with the drive letter :D like it always did, it comes up Local Disk :G and it says I need to format it. Is this some kind of virus or something? I cannot access the disk at all. I see the name in the disk manager, although it says it has 100% free space...and I know this isn't true considering last time I checked I had like 800gb left. I tried on 3 different computer and NONE of them recognize it, and I get the same formatting message. PLEASE HELP!!!!!!!!!!!!