Zero Turn Mowers

I have a M-ZT61 zero turn and have had no issues yet! I started it up great and mowed for the first time this year and after 20 minutes of mowing I set the speed to middle and turned off the deck then shut it off. When I returned to turn it back on (10 minutes later) it would not start. Arms are parked, Brake is on, Seat is engaged, PTO stitch is down(off) and it does not turn over at all. When I pull up the PTO the hours meter turns on and it sounds like it has power.
I left it off for a few hours but still no go!
Battery is 12.78V...Help?