Vehicle does not start

Hello,
My car suddenly stopped running. I was not able to start it. I tried jump starting but could not start engine.
I took it to the Infiniti dealer. He told maybe the battery was drained flat. So, he changed the battery, but still could not start engine. Then, he told me it maybe the ECM. He then told me he replaced the ECM but it shorted. Then he told me it maybe the engine wiring harness. He said it will cost about $3,000.00 for twenty hours of labor.
I have a feeling he is lying and would like an honest opinion. I am thinking maybe the ECM short messed up the wiring. He should have run a wiring test before putting the ECM.
What are you thoughts?
Thanks

Winston