Download DiskWave from here:
It's small in size and free.
Open DiskWave and go to the preferences.
Put a checkmark in "show invisible files".
Close preferences.
The DiskWave window shows you all your drives in plain English (no ridiculous graphical formats).
Click on any drive.
Now, you'll see what's ON the drive, listed in order of "largest to smallest".
You can easily locate what's eating up your space.