Gently prise out the switch with a flat blade screwdriver and have look to see if the plug is on tight, then unplug it and make sure the connectors are clean then replace, and see if it works, ideally you need a replacement to plug in and try because you could spend all day checking fuses and wiring but if that switch is broke the only easy way to sort it is to replace which should be cheap and easy from a breakers yard (not much help on a sunday i know).