Is this iPhone Completely dead?

Try hooking up a known good battery and chargeport (as well as the screen you have), plug it in and give it a few mins to boot. Once you’ve given it enough time to boot, try plugging it into a computer to see if the computer detects it.

If the phone is detected but the screen is still black it could be a faulty screen, or the phone is in DFU mode. If the phone is in DFU mode, when you open iTunes you will get a message saying “iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes”. To exit DFU mode, simply hold the lock and home button down simultaneously until the phone reboots, or if you don’t mind losing the data, click restore in iTunes. If the screen still does not show anything after this, the screen is probably to blame.

If your computer doesn’t detect the phone there might be bigger issues. With plugging/unplugging the device it’s possible that the charging IC was damaged, in which case it would need to be brought to a repair centre for microsoldering.

Hope this helps!