Same problem! The starter just clicked and chatterd at me. When that happened on my mower my battery had a few dead cells.
I replaced the battery and now it starts on the first crank. Good luck, Tom

Tom gives you the best place to start. If a new battery doesn't do it come on back. You can try your car battery with cables if you don't want to buy a new battery just yet. Disconnect both cables to the old battery and connect your jumpers. I always make my last connection with the ground to the frame rather than the battery terminal.

Might check your engine make sure the starter isn't stuck in the up position,turn the engine backwards by hand then try it ,or check your solenoid this is probably what's clicking.

Bob has the right idea. Before I purchased a mower battery I removed the old battery and jumpered in my car battery. When the starter kicked in I knew I had found the source of my trouble.
Then I went out and bought a new battery. Running great with no problems. Regards, Tom