I'm no mechanic but sounds like the starter isn't engaging, Does it have a solenoid? If so you should be able to bypass it, Can you turn the key to the on position and jump start it at the starter? Are you sure the motor isn't locked up, check the oil, Hope some of these suggestions help.

The steep hills won't necessarily harm your engine, but you must do a check of the engine oil every time, before you use it.An engine that has pressurized oil pressure would be preferable, but an engine without it will probably work. Also, just pulling out the oil dip-stick and looking at it does not suffice, in any case. you must set the machine level, pull out the stick, wipe it clean, then insert it and pull it out again, to get the true reading. This is because the oil will tend to stay high on the stick, even after setting for a while, and that gives you a false reading, without the double sticking procedure. Most mower decks i have seen, are stamped/formed steel(Tin) Some are heavier than others. Ya get what ya pay for. One of my friends has a lawn with some steep hills in itt, not long hills, but the way it was laid out wwhen the house was built. His older model John Deere is used to mow it, and it hasn't seemed to hurt the engine. The transmission/hydro is another matter. The original lasted 9 years, but had to be replaced last summer. JMHO: Rusty Jones

Put your part number of the blades it calls for in the Oregon site and it will list them as an option.

one possibility is the packard connector inside the molded wire plugs has failed. These are designed to exert pressure against the male spades that they plug into. The loop of metal has cracked or corroded and is not making contact with the spade. the link has a picture. http://www.ebay.com/itm/like/400341697381?ul_noapp=true&chn=ps&lpid=82