Passport Essential 700G Memory shows full but only had 100M of Data On it

My Passport Essential has been working fine for the past two years.  Now, for the past month or so, the Passport will not let me save to it.  It says it is full and when I look in properties it indicates the same (about 500 K free).  However when I look at the files individual properties I have a TOTAL of 200 M on the system.

When I delete files the properties shows no difference.

I have emptyed the trash and there are 0 k bites on that.  I have looked at hidden files and none are over a couple hundred K.

I am lost without that extra memory.

Can anyone help me?

THANK YOU!

Hi, try to backup all of the important files and the format the passport.