iPhone 5c completely dead, changed multiple parts

I have an iPhone 5c that's been sitting in the stock room for about a month. Nothing goes in there unless it's fully functional. Today we went to sell it to a customer and it's completely dead, won't charge, won't do anything.

Neither a new battery nor a new charge port will get any response out of the phone. No recognition in iTunes.

The charge cable is good, the charge port works in other 5c's and the battery is good. Still, nothing.

I'm stumped, and don't want to see this phone become a brick.

Any suggestions?