Why does my OP 3 shuts down after locking?

Hi there,

I recently changed the screen of my OP 3 because it fell on the floor and did not show anything afterwards (I don't know if this only damaged the screen or also other parts of the phone).

Now, the screen works very well and and the phone does turn on as well (I even type this with my OP3). But I now have two problems:

1) My phone shuts down almost immediately after I lock it (after one or two seconds I can still unlock it but after 5 seconds or so it is dead). It does not shut down while the screen is on, though.

2) It heats quite a lot during using and especially during charging. I know, this seems to be a general issue with older OP phones and happened to me as well, but never to that extent (after charging 30 min it gets overheated which never happened before).

Plus, there are two issues that might or might not be related to these to problems so I add them as well: My volume control buttons did not work before the screen replacement, which is quite odd, because the power button works well. And I think I have destroyed the home button/fingerprint scan while changing the screen.

What do you think, is there any hope of solving these problems without having to buy a new phone?

Best, thank you all!

Clemens