There could be many factors on determining what is wrong with your device. The two main concerns is that the battery isn't that effective or the motherboard and the charging port was disrupted and something shorted it. I think the only thing you could do without knowing what to do is to replace the whole computer, since the battery was replaced and still not working, and motherboard replacement could be expensive. Replacing the laptop means that at least you know you could get a new laptop without any issues.
At this point now that you can’t even load and get into your home screen, I believe the only thing you could do is factory reset the device and clear all the memory. Then restoring a backup of the data before the apps were installed if you have one.
The logic board (motherboard) could be damaged or it does not support your computer with the upgrade. Is the logic board the same brand as your old i3 logic board? It could be a software problem with the change of the logic board so maybe a motherboard bios update will fix the issue.
I also believe that this is a connector problem. Since there is little chance that the two keyboards have the same exact faulty keys, we could assume that the problem lies inside the connectors of the motherboard to the keyboard. Replacing the motherboard would be the best bet to continue to ensure a fully functioning keyboard.
According to your responses, the problem should lie within the battery or the power circuit of your phone. If the problem is the battery, you could contact customer service and maybe ask them to send you another one. If the problem lies within your phone battery circuit, you could maybe take it out to a technology repair shop and fix the circuit. I suggest first taking it to a few technology repair shops first to see what is actually broken so you could replace it.