[RIP]

I would suspect you have a common problem that's been popping up lately. The solder joints connecting the connector to the instrument cluster circuit board have cracked due to torque created by the connector's wire harness pushing up or down on the connector. When you smack the dash, the solder joints close temporarily, closing the circuit. Temperature will effect them as well. Take it to the dealer and they will replace the instrument cluster and charge you around $800. You can fix it yourself for the cost of a soldering iron and a day of your time. There is a tutorial on how to fix this somewhere on this forum. I'm sure someone will pipe up and give you the link.

You're asking how can this possibly keep the car from starting? The Chrysler Collision Detection data bus, better known as the CCD bus (consists of 2 wires) allows all the computers/modules in the van to talk to each other. The instrument cluster is a primary user of this bus. If this bus opens anywhere you'll see erratic instruments and/or starting issues. I'd bet the cluster solder joints have cracked, opening the bus.