Why won't the device power on after replacing charging board?

This unit had it's screen cracked. This was successfully removed and the replacement screen tested okay. i.e. the device powered up. Unfortunately the tiny menu and back button ribbons broke whilst removing the screen.

Obtained a new component to replace the charging unit including buttons.

Connected all back together again but device wouldn't power on. Took apart again and put the original component back in place but still wouldn't power on (I knew the original part did power on and screen worked so wanted to test if the new component was at fault).