Anyone any thoughts?
Yeah...
On computers any "switch", be it your keyboard or the power switch, is generally a plastic fascia to an actual micro switch beyond with an air-gap in the middle.
Thus you have two things that can go wrong... the plastic user-facing bit and the micro switch behind it.
On a typical desktop PC, you can take the front plastic panel off so you can get a proper look at both sides of the fascia switch.