iPhone 5s won't turn on after housing change

Hi have an iPhone 5s was in full working order prior to changing the entire housing, screen and home button as well as the lightening connector/headphone jack cable.

Now the phone won't turn on!?! I've tried pressing the screen cables and battery cable but still no luck.

I had a lot of diffiiculty removing the battery and had mid-shaped it but there was no visible leaks or holes so I flattened it gently and put it back into the phone..

So can anyone solve this mystery?? Thanks in advance :)