Craftsman Riding Mower Won't Start?

I'm new here and I've been reading through the "won't start" threads regarding Craftsman riding mowers. I have a 13 year old Craftsman 13.5hp 30" mid-engine riding mower, model 536.270280. It always has been a little balking when it came to starting during cooler weather (I'm in Pennsylvania) so when I tried to start it last weekend and it didn't want to immediately start I didn't panic. It was cranking, but I didn't want to flood the engine so I stopped for a few minutes. When I tried to start it again it tried to turn over but didn't (and here is a key symptom) when I turned the key to the off position, it kept cranking and trying to turn over for 10 or 12 seconds and then stopped. Now I get absolutely nothing. I tried jumping it, replaced the fuse and the solenoid is new. Still nothing. I was hoping to get some feedback before I start replacing everything. I'm currently thinking it might be the ignition, but that's just a guess. Any help is appreciated.