2001 mercury sable start issues

i have a 2001 mercury sable what im getting is its will not start but starts on occasion like today it started fine this morning did errands before work drove it turned it off short period and then started just fine and then drove to work after work it did not want to start tried every thing check engine light is not on and has not come on im am getting stumped i had to leave it in the parking lot at my work so my question is what could make it do this where it starts on occasion and then when sitting for a period of time will not start it cranks but just does not start

Since you say the engine cranks okay but won’t fire up when the trouble occurs the trouble might be with the crank position sensor, the ignition, or the fuel system. To see if this is a fuel issue carry a can of starter fluid with you so when the trouble happens again you can spray a small amount of the fluid into the intake. If the engine reacts to that you have found the problem area. If the engine doesn’t respond to that then chances are there is something wrong with the ignition area, which includes the crank sensor. Some folks have found faulty sensors that don’t create a error code.

ah thanks for the input ill keep you posted