I have a riding mower {MTD} with a briggs and stratton engine. I stopped to empty bags and got off mower without turning key just letting it cut off when I got off the seat. Now it won't restart. All I hear when turning key is a clicking noise. The engine doesn't turn over at all. It has never done this or even given signs that there was a problem. I usually turn key off but didn't this time any suggestions ?

It could be a dead battery, a bad starter or the switch that sends power to the starter. Try jumping with a car straight to the battery if that works get a new battery if not try the negative. End to the battery and the positive to the bolt with the red wire coming out of the starter(the cylinder on the side of the engine) if that works it's the swith, follow the line from the starter back to where it meets a black box and that is what needs replacing or u can contine u jump the same way and bypass the switch

Even before you do that, remove the plugs wire(s) and see if you can turn the engine by hand.

If might be time for a valve adjustment.

Battery issues are also possibilities.