it could be a cold solder joint on the toggle switch. you will havt to remove the board and have a look.
if it is, you may need to resolder it.
do this test. move the switch to mic and see if the line input still works. if it does, then the switch is bad. if it doesn't, it could be the solder or the circuit.
where do you live?i ask because you can send it to someone for repair if you can't do it yourself.