What lead up to this condition, was it dropped mishandled, water, Overheated on bed??!!!
if none of above test with a different but identical charger.
Best things in prevention to keep things cool is cleaning the fan & it's vents & adding new cpu heat-sink paste.
Since you are beyond that we have to guess at what the issue is with not much input except a few symptoms.
Suggest to start with removing the ram and putting in one at a time and interchange them to test if one is bad.
Next unplug the LCD from the logic board (motherboard and start laptop) Almost sounds like a wire is shorting from that cable or a ribbon that was not properly replaced in its socket, or perhaps the motherboard has some sticky stuff on it from spilled coffee or...