Lay the router on it's side with the base plate retracted enough to give you a clear shot at the collet and take a pin punch (not sharp on the end) and tap the side of the collet lightly where it's exposed. Rotate it a little after every tap. It sounds like you tightened the nut down with no bit in it which is something you should never do. If you are spinning the nut down on an empty collet do it by hand and the moment you feel the nut touch the collet stop!
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.