If the batteries are fully charged Here is a thought; Since you disconnected the batteries, have a good look to make sure you didn't forget one. On our 2002 Itasca Horizon, almost a twin of yours, I once disconnected a small wire while trying to figure things out just after we got the rig. I forgot to re-connect it. There is a sensor that won't let the rig start if everything isn't right, and in our coach it was wired directly to the batteries.
It cost me $100.00 for a service call and a missed ferry to find that out! :S