HD says only 3gb left but it's empty

I removed everything from my 500TB external drive to clean it out and begin again.  However, even though I took EVERYTHING off and transferred to another hard drive it says I still only have 3gb left.  Is there something I can do to reset it or something or is it trashed?

Thanks

Hello, 

Have you tried reformatting the drive? 

Where you using the drive as a backup destination?