no crank no start

Some time ago I bought an old Buick Lucerne 2006 (85k miles) as a project car. The seller said that the car is totally fine because the GM service run diagnostic, it only needs new ECM to be reprogrammed. It was definitely a pig in a poke but I bought it for really cheap so it was worth a try...

I changed my transmission in my 2011 Buick Lucerne cxl 3.9L V6 now it won't crank won't start and when I turn my key to try and start all dash lights go out and I loose power tell I stop turning the key I've checked all my connection, battery, grounds, starter, no luck can't afford to take it...