No display on M1330 laptop

I bought an M1330 from DELL in 2008 with nVidia 8400M and a CCFL LCD display.  Dell replaced the motherboard because of the nVidia 8400M problem in 2009.  it has worked perfectly since then until couple weeks ago.  One day, my daughter closed the lid of the laptop without shutting down the system.  Couple days later, we tried to turn it on, and there is nothing displayed on the screen(the screen is black and dark).  I did the following to try to resolve the problem:

1. I connected an external monitor to the laptop.  Everything is displayed normally on the external monitor (and nothing on the laptop screen), and I can log into the system and work normally.  If I push Fn and F8 simultaneously, there is a message "No external display is attached" displayed on the external monitor. 

2. The startup dagnostics gave an error message: error code: 2000-0321, unable to detect LCD on the external monitor.

3. Once I had another error message: Error code 5300:0023, VIDEO - no BIOS support for SMI interface function on the external monitor.  Updating the BIOS to A15 does not solve the problem.

4. By pushing the "power button" and the D key at the same time to turn the laptop on, the laptop screen entered some kind of testing state.  The screen displayed alternately white, red, green and blue color in full screen  twice, and I could see the backlight.  After that, the laptop started the normal booting process, and the laptop screen turned black (nothing displayed).  If I connect an external monitor to the laptop, everything is displayed on the external monitor normally. 

5. I removed the laptop keyboard and tried to tighten the connection of the display cables with the motherboard (video card), and it did not resolve the problem.

6. I bought an M1330 LED display kit (including the screen, back frame, bezel and cables) from Ebay, installed it to the laptop(The old display was removed).  No display on the LED screen either.

I appreciate any kind of help to address this problem.  Thanks in advance.