Black screen

Hey everyone,

I posted the other day about having the black screen after installing new RAM.  The discussion so far is here: 

https://www.dell.com/community/XPS/Studio-XPS-15-1640-memory-upgrade-issue/m-p/7194133#M23944%2Fjump-to%2Ffirst-unread-message

I have hooked it up to an external monitor.  Everything worked great.  I ran diagnostics after hitting F5 on start up.  All checked out and passed, including the inverter and LCD.  I am at a loss.

Anyone have anyideas of what to try next?  Could I have knocked something loose?