If the windows start working when the door is moved then it will be a break in a wire where it passes from the body to the door through the rubber protective grommet or near to this area.

As for the horn and sidelights I would start by checking the fuses, if they are ok it mite be worth looking at a wiring diagram to see if the two circuits share anything in common (earth, splice in wiring etc). Is it just the front sidelights that are not working? If so this would eliminate the switch.