You have tried quite a lot of combination to make sure there could be a problem with the board.
As last resource (if you have not done it yet), you may try to do a bios recovery.
Note: For bios recovery, video on screen is not always available, it can even work without video as you do not have to do anything once the system is started.
Briefly, it a very simple procedure.
Just before you do the bios recovery, try clearing the cmos again, removing battery and power connector and put them back after about 30 minutes.
Download the recovery bios from this link: http://downloadcenter.intel.com/license_agr.aspx?url=/17417/eng/CB0075.BIO&ProductID=2933&agr=Y&sType=&PrdMap=&DwnldId=17417&strOSs=38&OSFullName=OS%20Independent&lang=eng
Note: It's not the latest bios, if you manage to get video, then you can update the bios later.
Put this downloaded file onto a non-bootable (FAT32) USB pendrive or an empty cd (non-bootable). This should be the only file on the cd or usb.
Connect the usb or put the cd into the system, connect only processor and its fan, power supply, 1 stick of memory, keyboard, monitor (onboard only).
Remove the bios configuration jumper.
Start the system. The bios recovery should start automatically and you should see the activity led on the cd drive or the usb blinking meaning that it is recovering the bios. It may take sometime. Once you do not see any activity, you can shut down the system, put the bios jumper back to the normal position and start the system. If you still do not have video, then there is no other way that to RMA the motherboard.
Contact you reseller to get the motherboard replaced.
Hope this will be useful.