If the system isn't drawing power from either and won't start, it is indeed likely a system board issue.  
Hi All,    I'm in the process of trying to help out a colleague. His XPS 7590 is a few months out warranty (naturally) and wasn't switching on at all. After pulling the RAM I finally found that one of them was faulty. Its now out and the laptop will boot HOWEVER - it won't charge the battery at all. I've run a multimeter over it it's getting 19V @ the DC in on the motherboard. Worth mentioning here that it also won't run unless the battery is connected - absolutely nothing with battery disconnected. Any thoughts? It sounds like the motherboard to me but i'm no IT support. Is there anything else I can check? Cheers   Rob
Dell 7590 XPS won't charge, 19v at DC in