Low oil pressure no start - 2003 Lincoln Navigator

CHECK ENGINE OIL LEVEL ON OIL DIP STICK.OIL LEVEL SHOULD BE ON FULL MARK IF NOT ADD OIL UNTIL YOU GET TO FULL MARK.IF OIL LEVEL OKAY.YOUR LOW OIL PROBLEM CAUSED BY WORN DAMAGED OIL PUMP OR WORN ENGINE CRANKSHAFT BEARINGS.IF OIL HAS NOT BEEN CHANGED A LONG TIME CHANGE OIL AND OIL FILTER NOT GUARANTEE TO FIX PROBLEM.BUT COULD BE MINOR THING.OIL FILTER COULD BE STOPPED UP.WEAKEN OIL FLOW BUT LIKE I SAID PROBLEM COULD BE OIL PUMP OR ENGINE BEARINGS.REMOVE OIL SENDING UNIT SCREW IN A OIL PRESSURE GAUGE.TURN ENGINE OVER SEVERAL REVOLUTIONS TO SEE IF OIL PRESSURE BUILD UP TO 40 LBS. SEE 40 - 60 PSI. 2000 RPM.IF NO OIL PUMP TO WEAK .IF OIL PRESSURE RISES WHEN TURN ENGINE OVER.I HAVE SEEN FAULTY OIL PRESSURE SENDING KEEP ENGINE FROM RUNNING BECAUSE OIL PRESSURE SENDING UNIT WILL DISABLE FUEL PUMP RELAY TO KEEP FROM DAMAGING THE ENGINE.

Oil pressure will be low until it starts. You don't give enough info to get help. Does the engine turn over or not? Does the ignition click, buzz, or do anything? Is the car either in Park or Neutral (try both). You'll have to push the brake pedal down to get it to start in neutral.