What is wrong with my Panasonic microwave?

I have a Panasonic NN-E548W microwave. The light stays on even if the cooking time has finished, (or even before it has been set). (I was going to add that the turntable turns also, but I have just discovered that this seems to have fixed itself). However, it was never cooking when in this state.
This all started after my lodger had a bit of an accident with a large liquid spill some months ago, (easily long enough ago for it to have dried up now), but I can't be absolutely 100% sure this caused the problem. Can anyone help please?