remove spark plug(s) - tie back spark plug wires - crank engine - watch for any fluid expelled thru plug hole(s) indicating a hydrolocked condition. If so, determine cause of fluid in cyl and fix. If water or fuel, drain/refill engine crankcase oil/filter before running same.

If all OK above, replace plugs and crank engine. If engine refuses to fully turn over then, first recheck the electrical starting circuit: Get the battery LOAD tested by a qualified shop; Take apart and clean to bright metal all contacts surfaces in start circuit wiring (battery posts, start solenoid, chassis grounds, starter posts).

If machine was left out in weather, may also have accumulated water in starter casing,etc... post back with results. good luck.

It turns out it was the battery after all. A friend suggested I try checking out the amps or jumping it even though the voltage looked fine (my multi won't test above 250 mA). Anyway- jumping it worked. I ran it for about an hour mowing. Turned it off to get more gas. Had to jump it again to restart and mowed for another 40 mins . When I came back later in the afternoon for a third go it started without a jump.

Leads me to think either something is vamping the battery, or the battery just slowly discharges. Either way the main issue was resolved.