If its damp outside when you are trying to start the car then you might be losing voltage from the ignition coil to the spark plugs especially if the ignition wires are old and dirty. Moisture on old or cheap ignition wires can cause the voltage to bleed out of the wires and short to a ground.

Try wiping down the coil top, coil wire, distributor cap and the spark plug wires with some dry paper towels before you try starting the car.

Be sure that there is no oily residue on the coil tower. Pull the coil wire off of the coil and wipe the top of the coil clean. Also wipe the inside of the coil wire boot.

This whole process should only take a few minutes.