Back up all data if you haven’t already done so. Before proceeding, you must be sure you can restore your system to the state it’s in now.
Launch the Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, press the key combination shift-command-U. The application is in the folder that opens.
☞ If you’re running Mac OS X 10.7 or later, open LaunchPad. Click Utilities, then Terminal in the page that opens.
Drag or copy – do not type – the following line into the Terminal window, then press return:
sudo ls -ARl .Trash /.Trashes /Volumes/*/.Trashes
You'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning not to screw up.
The command may produce a huge amount of output. If it does, stop it by pressing the key combination command-period, or closing the Terminal window.
The output will be a list of files that are in the Trash, including files you can't see in the Finder.
If you're sure you want to delete all those files, following the instructions here:
You can't empty the Trash or move a file to the Trash
