Files not showing on external drive

My xternal drive is showing 639 GB used with 290 GB free space.  My hard drive is only showing a few files that add up to about 2 GB.  How do I get back all my lost files?

Look in Disk Management down where the bars and see if it says anything like Raw and the color of the bar.


Sorry, I have no clue what you just said.  What bars? Where is disk mngment?