What device casing can be used to replace the damage bottom/back casing of this laptop? Where can replacements be...

Turn the printer in an unusual way. Like on its side or upside down. If you can shake it a little. There may be something small lodged somewhere inside. There may be nothing lodged inside but maybe residue build up is causing the problem. Use sparingly alcohol whipes.

If still under warrenty carry to nearest store ot designated repair shop amd have them take a look. Alternatively, open device and check that the screen is connectors are attached properly. If the connections are OK then there is likely fault with the display glas. It should be replaced.

Battery and zigzag (lightning) symbol usually means the device is charging. Im wondering if this weird version of the symbol means that it's charging slowly/less efficiently. Since it's plugged into another device most of the power may be reserved for transferring files. Try using a different connector cord or go into your laptop settings to change what the connector cord does. (Change default USB connection settings. Try disabling and enabling the USB port to see if that changes anything.