I was driving to work the other day when my truck lost 15 psi in oil pressure, it **** off and came to a stop. Now there's oil leaking out from behind the power steering pump and around the pan and also it now won't start. What is wrong with it?

 

I take it from your statement that you have a mechanical oil pressure gauge. How else would you know you lost 15psi of oil pressure. Well, if you have a full complement of mechanical gauges, as I assume you do, you must monitor your engines performance constantly. That would lead me to believe you are mechanically inclined. I would believe that you are, if it was not for this totally simplistic question that you posted.
I guess I have a reputation for not having tolerance for questions like this, and, a habit of being sarcastic. Oil pressure will usually drop when an engine shuts down. Did your oil pressure drop immediately before your engine "stopped", or was it 10 seconds, a minute, an hour, day, week, or other?
As far as the oil leak behind your power steering pump, it's probably your power steering pump. It could be leaking, and blowing due to the fan, onto your lower engine. By that, I don't mean the engine below your engine, I mean the lower part of your engine, which would consist of your oil pan.
So, as far as your main question goes, "what is wrong with it?", judging from the plethora of information you gave, I wouldn't have a clue.

 

Seriously, you should start by downloading the service manual. This is available under Weedahoe's signature. I say this only because my wife says I sound mean!!!

 

I am sorry to say. there is almost NO information...

we did not drive it, or hear it, can not look under the hood. Not able to smell it..

 

Lost oil pressure
leaking bad behind PS pump/oil pan
won't start

Sure you didn't break a piston rod and throw Iit through the pan or out the side of the block?