Why wont my truck start

Same with any no start , check for proper spark , fuel pressure injector(s) pulse . Something may have gone wrong by pure coincidence . Could very well be ignition module .

When that happens the charging system sends out a voltage spike that kills electronic components. So brace yourself for an expensive repair. Now having said that the security system also activates when main power is disconnected, so you could be dealing with that, shut down procedure is listed in the owners manual for you vehicle. Good Luck

If you know enough to find a separated battery cable connection and reattach it, you probably know enough to check for blown fuses; look in the box under the hood and inside the truck. There are fuses associated with the engine and there's the big mega-fuse that goes to most of the car. See if any are blown. After the cable fell off it likely sparked or when reattaching the cable it did this, and you likely just have one of more fuses that need to be replaced.

check mega fuses under the hood if applicable

Most likely the PCM is fried because of the power spike of the battery becoming disconnected. If you're lucky only the 100 amp MAXI style fuse is blown. Look for it in the underhood fuse box. It's one of the big ones. Hope that helps! Jim