I have an 04 F150 FX4. This truck has always been dependable. I have right at 474,000 miles on it and it has never had any actual problems until now.
The truck will randomly not start. You hit the key and everything comes to life like it should but the starter wont do anything. I originally thought it may have been the starter, but the 2nd or 3rd time it happened I was moving the key slowly back from the start position to the run position and the starter kicked in. So I figured it was the electrical part of the ignition switch. Installed a new switch and all seemed good and 4 days later the same thing.
My next thought was the starter since the solenoid is on it I thought it may have been a bad starter or solenoid. With that replaced I felt like it was handled and 3 days later, I go out to the truck,and no start. And when I say this is random, it is very random. The truck wouldn't start this morning, but I am willing to bet that it will start when I get home this evening. I am probably missing something very obvious, but I haven't found it yet.

 

Wow! 474,000 miles! Amazing! You have changed all the obvious, sure sounds like a bad starter. Have you checked the battery, do the gauges act weird when you turn the key on?

 

I have checked everything that "I think" is obvious. The gauges act normal and everything else seems normal. The only possible thing left in my mind is maybe a neutral safety switch that is starting to go out.

 

I would check the FDPM as it may be the problem not getting enough fuel pressure to fire the engine up. As they been known to go bad for where they sit right behind the fuel tank on the frame right in front of the spare tire on a cross member of the frame. The case it is in cracks and dirt and moisture can get on the circuit board causing it to fail may be intermittent like what you are describing.

 

I am pretty sure it is not fuel... The engine won't turn over. And sure enough, I just got home from work and hit the key she fires up like nothing is wrong.