Words mean a lot, since that's all we have to communicate.
On the 2nd battery, "still nothing".
I'm sure it clicked or groaned or made "some" sound.
What did it actually do?

I'd remove the spark plug and see if the engine will spin.
Possibly hydro locked?
There may be an electrical issue, but the first test is quick & easy to do.

Bill Thank you for your quick response. I recharged the new battery and tried to start the mower so I could tell you exactly what noise it was making and it started right up. So I guess I need to remove my post. I will probably be back as I have no ideal what killed my 1st battery as the mower was starting easy and running good until that happened. Again thank you. Robert

Your tractor only has a 3 Amp charging system.
That's pretty marginal for charging a depleted battery in a reasonable amount of time.
Theoretically, it would take 10-12 hours to fully charge a totally discharged battery at high engine speed.
Chances are your 1st battery simply failed and the 2nd wasn't as charged as you thought.

I had a car battery short out in front of the supermarket once. Car was running, shut it off to load groceries, then nothing.