There could be different key combinations to change input, check samsung guide somewhere on google. I mean after connecting external monitor via hdmi or vga,
Try reseat ram, do this while power cable and battery is out. Test with 1 ram stick in each slot and add power cable after swapping to test each time. Always remove cable after trying.
Did you update bios before this happened ?
If you plan disassemblying further and there is no warranty and your ok with risks then here is video how :
https/www.youtube.com/watch?v=LMchetePFo8
Tell me if you plan on disassembly so i can help more, otherwise go with what skynetrising said.