Studio XPS 1647 laptop POST LED error codes

(Posted this a few days ago but got no answer. Try it one more time.)

Symptom:

Studio XPS 1647 laptop can't boot past POST and stuck at Dell splash screen with progress bar at ~80%. After holding down FN and pressing the power button for an ePSA boot, all three volume LEDS would flash twice, immediately followed by the MUTE LED flashing and then going off, followed by volume UP and DOWN LEDs flashing and the volume UP LED going off, and then followed by just the Volume Down LED flashing continuously. The fan is turned on immediately after the PSA boot with slow speed, and then it spins faster after a few seconds with louder noises.

Recently my Studio XPS 1647 has had overheat problems, and sometimes they would cause BSOD. A reboot after BSOD always showed broken screen images. The BSOD always came with bcode 116 error: this is apparently video card related. So last weekend I opened the case, removed the heat sink and the fan. The heat sink vent was completely blocked with a thick layer of dirt, so it's no wonder for overheating. I cleaned up the heatsink vent and the fan, cleaned up the top of CPU chip and the top of GPU chip, reapplied thermal paste and put everything back together. After that, the machine couldn't pass the Dell splash screen on boot.   I've already checked the discussions and followed suggestions on holding  down the power button to remove static, reseating the memory card etc., but they are of no help.

The following video shows the POST LED lock codes:
http://youtu.be/l0zbweEeCYY