Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accurately.
Is you theft light flashing rapidly?
If not with the key on and engine off is the check engine light on? If so when you crank the engine does the light turn off?
Ok, there is not much we can do but we will try anyway. Your problem is your computer is not getting power or it is bad. Look in the fuse box under the hood. Here is a pic.
Now try swapping the two relays highlighted in red. If it starts replace the one that was the pcm power relay. If it still won't start you are going to need to take it to someone that can test wiring to find out where the power problem is. If there is no power problem you are going to need a new pcm. I would suggest having a dealer do this work because they have to program the new pcm and also need to program the antitheft system so the truck will start.
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I'm sorry but without some basic test equipment I would just be guessing as to what is the cause of your problem. I think you next step needs to be to take it to a shop.