This may be a far cry from your situation, but I had the same thing happen to me yesterday when I went to get our rig out of storage.
I had the batteries all disconnected for the winter. I recabled them up just as I had done every year. Went in to start it and nothing. Completely dead. I did have 12v to the "house", but nothing to the chassis. Checked battery disconnect switch in the engine compartment, and it was on.
Rechecked my connections and found the end of one large battery cable laying in the back of the tray behind the batteries. I missed it when re-cabling the chassis batteries. Hooked it up and away we went.
So, I guess my suggestion would be to check your cables and connection to your chassis batteries.