External Hard Drive appears empty, even though it's almost full

Hello,

My External Hard Drive has almost 2TB of Data on it.
Last week, I opened it and it says 'This folder is Empty'
However, it does state that only 66GB of space is free so my files must still be there.

I've tried this in Cmd Prompt:

attrib -h -r -s /s /d l:\*.*

BUT all it says is 'file not found' (note: l is the letter assigned to my hard drive)

Any and all help is appreciated :)

P.S. I'm not very computer savy so please dumb things down