To resolve the error: Press the On/Off button on the printer control panel to turn off your printer. Wait 30 seconds. Press the On/Off button to turn on your printer. If the error continues, double-check that all paper and foreign objects are removed from inside your printer, then follow the link below. NOTE: Even if you do not physically see a paper jam, you will need to follow the paper jam link to solve the error.
Let's start by running msconfig.exe. On the start tab click extended options and uncheck the maximum memory option, if it's set. If that's not set, run resmon.exe and see if the missing 4GB are "hardware reserved". That means simple, that it's a faulty stick and windows could not write to it (bios only reads the spd config but does not check the ram itself).
Yes you will need to replace the Ltd screen on the device. There are some excellent tutorials on this website that you can follow. If not might be best to take it to a shop for repair.
I have seen this problem many times most of the time this is due to a loose connection on the display and the motherboard. There is a very good tutorial on YouTube on how to open these might be worth checking the connections before you buy a new screen.
Check your charger, which might be faulty. If possible check the charger on another device and if that works there is an issue with your device. Check the connection to make sure nothing is stuck inside e.g dust or fluff. If that fails then it's either a battery of connection.