91 2.3L won't start

My 91 2.3L mustang quit starting last night. It was running fine until I stopped by a friends house. When I was parking I did a pretty good curb check that jostled the car a bit, but didn't think it was a big deal. Go out to start the car and get some clicking then nothing. I had dome lights and a few dash lights stay lit but the horn sounds like it's dying. So, figure it's the battery or the terminal posts. Remove cables, clean them REALLY good with terminal cleaners inside and out and put them back on good and snug. Nothing, not even a click. Then, get friend to jumpstart me, get a click and it kinda tries then nothing. He did a bunch of wire tracing and stuff in my engine compartment and said it all looked ok. We didn't look at the starter though. The starter is less than a year old though, so I really don't think it's that. Anyway, I'm at a loss as to what to do now, we even tried to push start it (it's a standard, used to work all the time) and nothing. Anybody have any ideas? Thanks