[oldguy]

Check for a plugged fuel tank vent. also may need to get the injectors cleaned and checked for leakage. could have one with some gum/varnish not seating and leaking fuel down the intake. Especially if the tank vent system isn't working. just sitting in the sun can build up fuel vapor pressure in the fuel tank.

 

[oldguy]

pull a spark plug in each cylinder, then try cranking, might have a cylinder full of gas stopping it. Also put a voltmeter on the battery while trying to crank, if it drops way down, battery is discharged.

 

[oldguy]

fire extinguisher handy just in case...