If you can't recover them from dropbox a tool like recova (http://www.piriform.com/recuva http://www.piriform.com/recuva) might be able to recover them from you

If you can't recover them from dropbox a tool like recova (http://www.piriform.com/recuva http://www.piriform.com/recuva) might be able to recover them from your hard disk (when a file is deleted it isn't really erased, just a pointer gets deleted)