My trash will not empty the file that is in it. The file is neither in use, nor is it locked.
Emptying the trash produces that familiar sound except that that particular file will not go away.
I once followed an online article which involved using Terminal but it didn't help.
By "not locked" do you mean that you clicked it, hit Apple-i, and checked the ownership and permissions so that you have read and write permission?
If you've already done that, I suggest altering the file name. Add ".txt" to the end (or replace whatever extention is there already). It should change to a text document. Try erasing it again. If that doesn't work, reset your computer and try it again.