How long have you owned the device for? If you've owned it for under a year, go to Apple and they will replace it with a new one as long as there's no physical damage and as long as it hasn't been serviced anywhere. If no warranty or apple care I'd recommend minhos answer.
Find a local reputable repair shop, give em a call and ask them if they can diagnose your device and possibly find a solution. Usually it's a battery problem, then again could be something else. I hope this helped.
The best thing to do is this, first, get the model number, usually you can find the model number it was packaged in, of the box, or some place where the battery sits in, I wouldn't be too sure but should be easy to find. Once you find that, go on ebay or amazon, in the search bar type this “(model number) battery replacement" that should give you what you're looking for. I hope this helped.
I've honestly never seen that. Here's a couple things I would try. Triple click the power button, you might be using disability assist. I that doesn't work, reboot your device. How to reboot, press the volume up button, then down button, and then press and HOLD power button until the display goes black and once you see the apple logo, let go of power. You want to press all the buttons back to back, like counting from 1 to 3. I hope this helped.
The microphone for calls would be located on the bottom left loudspeaker grill. The 2nd microphone for siri is on the proximity sensor flex cable, located right under your ear speaker on top. Finally the 3rd microphone is behind the device near your camera, it's a small tiny hole, used for picking up sounds when you're recording a video. I hope this helped.
What's the model on the tablet? Usually it would be behind the device or on the packaging it was in. Sounds like the LCD behind the digitizer is damaged from impact. Go to ebay or Amazon and in the search bar type up “(model of the device) LCD screen" and you should get a search result kn the cost of the replacement part for that particular model. I hope this helped.
Does it turn on with the original battery connected? Or did it ever? Try this, install display with new battery, wait 15 seconds, that's about as much time as it needs to boot up all the way, after 15 sec, turn the vibrator button on and off, and if you don't feel a vibration, battery is bad, if you do feel a vibration, lcd screen is bad. Try a new battery, if new battery doesn't work, check by the battery connectors you will see some small components closest to the connector, you might have broke off one of those components while prying the battery up. I've done that before and it's not easy to deal with if you dont have micro soldering experience. If that is the case try to find a repair shop around you that has micro soldering experience with this issue. Always disconnect the battery from the left side of the connector with a spudger under the flex cable. Hope this helps.