Failure to Empty Trash
You could try using terminal.
I suppose that you can not remove the files from external drive trash (Mac use separated trashed for each drive). 

In order to remove external drive files try this:


Open Terminal
Write: cd /Volumes/{Your External Drive Name}/.Trash
Check that your files are there with: ls -la
Remove them using: sudo rm -rf ./*
It will ask your password


With that you should be able to remove your files.
You can do the same for your local drive but the .Trash folder is on your user folder instead of the drive root.