2002 Dodge Durango My durango turns over but won't start

I just replaced my ecm last week, the vehicle started right up and ran like it was brand new again. Then after 50 miles the check engine light came on & I went to Auto Zone to have them run a diagnostic check on it, it said bad Internal Control Module (memory loss). He said he never saw that before & since I just put a new computer in it, that it might be the problem & the light should go off eventually. Before I replaced the ecm, the odometer went off & it read "no bus", put the new ecm in & it worked great. Now when the square indicator around the P doesn't light up, along with no idiot lights on, the truck won't start (3 times this weekend). When the check engine light is on & the square indicator is aroune the P, it fires right up! I would appreciate any help.