My Truck won't start

you probably left the battery plugged in while it sat. The battery will drain. If you take your cables off and let it sit it wont hurt nothing, it still maintains it's CCA ability. Charge it back up and see what happens

You say: My 2003 ford Explorer wont turnover, after sitting for 5 Months and my Starter, Alternator, Battery & Fuel Pump is gd? #1 Even if the alternator and fuel pump were BOTH BAD it would not keep it from TURNING OVER. #2. If it won't TURN OVER how do you KNOW the starter is still good? #3 You didn't mention the starter SOLENOID, the IGNITION SWITCH or the NEUTRAL SAFETY SWITCH. If any of those are bad the starter will not be able to turn the engine over. Lets pretend all those parts are ok. You didn't mention trying to turn the engine over by hand with a wrench on the crankshaft bolt to be sure that it isn't locked up. Do that before trying anything else. If it turns freely by hand that eliminates a lot of possibilities. This is a 2003 vehicle, its VERY likely to have issues with corrosion, which can easily effect many of the electrical connections, including those in the starting circuit. A bad GROUND can EASILY disrupt the starting circuit. This is HIGH PROBABILITY for an older vehicle that has been sitting for months Unless you KNOW they have been replaced VERY recently, check and clean the 18+ YEAR OLD positive and negative battery cables-BOTH ends, as well the cable from the starter solenoid to the starter itself. Also check and CLEAN the ends of the ground straps AND where they attach to the engine or to the frame or the body. This is routine maintenance, so even if it doesn't fix the problem it will eliminate a lot of potential electrical problems.