Time went by - experienced the Error 55 on my ASUS ROG Board as well...
It happened when trying to put an IVY BRIDGE CPU onto the Z68 Board:
No sound, no picture.
And sometimes it's really necessary to find out, what the booting process does "next".
It held at code 55, but the RAM was fine.
The error was the CPU MISMATCH, because the BIOS VERSION was too old. So the LED just stuck in the latest step before the error occurred.
Thank god, ASUS offers the USB BIOS FLASHBACK, which allows you to (re-)set your BIOS on a blank board (without CPU, RAM etc...)
Due to the fact that i found uncountable different hints for this:
a) Find USB Stick (max 4GB) and format it to FAT32
b) Download latest BIOS Version on ASUS Page
c) Download the Bios Renamer (Bios Tools) for the same Mainboard
d) Put Bios (.rom or .cap) and renamer on stick. Renamer does nothing than rename the file to a specific mainboard shortname (e.g. M4EZ.rom for the Maximus IV Extreme-Z...)
e) Find the ROG Connect/ BIOS Flashback USB Port on the Board and put the Stick in.
f) Push ROG-Connect / BIOS Flashback Button for at least 3 seconds.
g) The BIOS LED on the Mainboard should blink for about 3 Minutes, (if there is none, the button might blink) - BIOS Flash is finished.
h) No Blink means that there is a BIOS mismatch, filename mismatch or the USB Stick is broken/too large/wrong format.
And - to close this up:
Experiencing a blue screen when exchanging mainboard and cpu when restarting windows might be a result of a misconfigured sata controller. Open BIOS and make sure that the configuration sais IDE and not AHCI. After installing the matching ahci drivers for the mainboard, you can switch this setting back to default.
Hope that helps anyone with the same issue.