Cannot safely remove my Passport from my Dell Laptop

When I try to ‘safely remove’ my Passport external drive, a separate window pops up to say that the drive is in use and that the application is still using the Passport.  I have checked any running programs and there are not any running.  I turned off my Microsoft Security Essentials as well with no luck.  Is there anything else that I can check to somehow safely remove the drive?  Thanks for your help!

Turn off your computer then remove the drive. Also try to check if a backup software is using your drive like windows back up or wd smartware.