RPMs spiked while driving then rough idle.

Hello all,

Was driving my 2001 Ford F150 5.4L on the highway when suddenly the RPMs spike when pressing the throttle. Immediately pulled over and the the idle was all over the place. Shut the car off to see if anything looked wrong under the hood. Tried cranking the truck again and I could hear the engine turn over but it would not start. Tried looking at the accessory belt as it was trying to turn over and it did not move. Got it towed back to the house but I'm kind of stumped how the engine can turn over but it won't start and the belt isn't rotating. Thoughts on what I should look at on the truck?