Why are my Switch's POWER button and volume buttons not working?

Me and my dad have tried to replace the battery and fan of the Nintendo Switch, thinking that it should solve the issue of it overheating and running out of battery faster than it used to. Before the Switch was working again after reassembly, we needed multiple attempts to fix the issue with the card reader and touch screen not working. We identified another problem that we may tackle later, but then something else happened.

I turned on the Switch, but when I tried to make it go to sleep mode the button didn't work anymore, and later on I discovered that neither did the volume buttons. Luckily, the same functions can be found in the quick menu accessed by holding the HOME button, but right now the only way to turn it off is to wait for it to run out of battery and multiple buttons not working is a problem in itself. What could have happened?