I’m pretty sure you’ll be able to find the back cover on eBay, make sure you got the right tools to disassemble it. You can also try to super glue the screw post back in place and maybe some double sided tape around all the edges of the frame.

If the warranty does not cover accidental damage, you may need to consider getting the screen repaired at an authorized service center or a trusted repair shop

It could be the flex ribbon cable, most likely due to outside pressure on the screen or a drop

it’s hard to tell on the picture, but maybe your battery died of old age

There are a few things you can try first: (1) Restart your phone. This is often the simplest way to fix minor problems. (2) Check your volume settings. Make sure that your phone's volume is turned up and that you're not in silent mode. (3) Clean the speaker grills. The speaker grills on your phone can get clogged with dirt and dust, which can block the sound. Use a soft brush or cloth to gently clean the speaker grills. (4) Update your phone's software.Sometimes, software updates can fix bugs that cause problems with the speakers.

The keyboard itself usually has a flexible plastic circuit with silver painted traces. If these traces corrode, crack, or the plastic rips somehow, it will break key groups (rows or columns)

Install YouTube Outside of Play Store

What is a dialing problem? Is it dialing numbers by itself ? If that’s the case your phone screen is faulty

Try resetting the video signal. Press and hold the power until it shuts off. Press and hold it again until you hear two beeps. Im guessing you have tried different HDMI cables and another display. If the resolution that the previous owner has set doesn't work with your TV it will do this.

If your phone has 2 SIM slots it means you have the international version, which in the US it has trouble connecting to 5G networks. If you have the US version try and reset the network settings