This post is quite old now but here's what worked for me:
Step 1: Disassemble the machine to get access to the bios chip
Step 2: Desolder the bios chip using a hot air soldering station(important!!)
Step 3: Reflash the chip with a dump from another machine using a CH341A programmer or similar(verify the flashed image)
Step 4: Solder the chip back in and reassemble the machine (the machine will still not post, but if done correctly, the bios backflash function using a USB stick should work again)
Step 5: Using the bios backflash method, reflash the bios(if I'm not mistaken I took the A05 bios)
Step 6: If the flash was successful your machine should work again. If not, repeat the process. If it's still not working there might be some other serious problem.
My theroy is that this bios setting mentioned in the previus post bricks something in the Intel Management Engine. As far as I know the Intel Management Engine is responsible for the bios backflash function(which did not work at all prior to the manual bios flash)
I hope that this post is not too confusing and may bring some Alienware's back to life :D