Device dead after LCD assembly replacement - no vital signs

Hello everybody, here is my issue, maybe somebody has already been in my shoes.

I replaced a LCD assembly on a cracked glass Xiaomi Mi Mix 2, fully working otherwise, and something has gone wrong since the device can not power on anymore. No LED, no vibration, no detection when connected to a computer, no response whatsoever.

During the removal of the battery I accidentally broke the underneath adhesive tape so I had to pry the battery out; in this process I damaged the battery shield, which failed internally making some smoke but not taking fire, luckily. The battery connector, however, had already been detached from the motherboard,

I ordered a new battery and reassemblied the phone, but the device could not power on. I initially thought that the new battery may had been too low level and left it on charge for two days, but it seems not to change anything.

Any thoughts on what to do..? Should I try a second, new battery? Is there any check I can do? The internal connectors seems all to be in place, and the other parts shows no visible damages.

Thank you for any suggestion, I appreciate.