Question : Problem: Laptop works remote monitor but not onboard LCD screen

2 month old Dell D820 laptop wouldn't get past the power light illuminating on boot up two weeks ago.
Called Dell tech support - went through several troubleshooting steps - (all the normal loosed connections, loose RAM, etc. etc. etc.) - finally decided it must be board level.
They sent out a replacement motherboard the next day with a tech to replace it.  Same problem.
Tech called the facotry - decided there may have been a firm ware upgrade - they sent another motherboard (#2).
Next day - tech, motherboard & new CPU arrive - changed out - same problem.
Tech called the factory.  They offered to replace the laptop "in about a week".  Frustrated - but no other solution - I accepted.
Two days later - called to verify that the order was in process - no one could tell me what the status of the order was.
Anyway - Dell sent tech #3 with a plethora of parts - motherboard, RAM, keyboard, LCD screen - it "seemed" to heal with the new LCD screen - BUT failed again the third or fourth reboot - identical to day #1 failure - back at the beginning.
Tech support said they had gone as far as they could and I would have to wait for the replacement ---
BUT - shortage of 15.4" LCD screens would delay shipment 10 - 15 more business days once the laptop was ready.
Argghhh!!!  ????
Tiral & error - found I could unplug the laptop monitor and run a remote LCD monitor via the VGA port - now the laptop became a desktop that looks like a laptop.

Finally requested a new screen that I would install in hopes of a work-around.
It arrived Tuesday PM (2 weeks and 1 day after initial failtuer).
Install went very smoothly - by the book - but now --
when it boots - it does not "see" the onboard monitor.
The system thinks the remote monitor is the onboard one.
Display Properties shows "multiple monitors" but "Identify" only sees the remote.
Attempting to toggle between LCD & remote brings up a message telling me no "remote" monitor is found.

Ideas?

Answer : Problem: Laptop works remote monitor but not onboard LCD screen

1. Try to reboot with the secondary monitor unplugged from the laptop.  
2. Try to reboot in SAFE MODE witht he secondary monitor plugged and unplugged.