Ok I am more awake now
Right so you have put your pc back together in the Rampage II Extreme board and you still have no video display.
Right do this and report back.
Check each stick of ram on there own to see if any of them are faulty.
Then take the cpu out of the board and make sure there is no thermal paste on the bottom of the cpu and on the pins.
Then disconnect all drives etc and see if the post screen comes up.
You are going to need another graphic's card to test it with aswell, also try another power supply as well as the power supply could have gone faulty if you have plugged the wrong power connectors in to the board.
Trust me though forget about the Rampage 3 Extreme board get a Gigabyte UD7 board.
I have had the following:
Rampage II Extreme
Rampage III Extreme
Gigabyte EX58 Extreme
The Rampage III Extreme kept giving me IOH Overheat issues and other issues and in the end I had 6 of them in the space, of a week all faulty and all got returned after the 6th failed I got my money back and, went back to using my Rampage II Extreme board and spent the money on a new GTX 480.
My Rampage II Extreme then started to have issues with the ram so I had to send that for repair and it, turned out that a pin was bent on the board and that was causing it not to pick up a stick of ram, then I got that back and then used that till last month when it decided it was going to start messing up this time it was a sound fault, in the fact it does not like my sound card.
So now I am running my Gigabyte EX58 Extreme board and have actually found that my chip can run at a higher overclock, and also my ram runs at 1950mhz instead of 2000mhz which is due to the overclock, whereas in the Asus board it would only run at 1600mhz.
As you graphic's card now appears not to be working even in the Rampage III Extreme board, then maybe your Rampage III Extreme board is not faulty after all and it could be one of the following or a combination:
PSU
RAM
HDD's
CPU
I wish you luck with this as I am not the most patient person as some people know, but by now I would of lost it and thrown the lot out the window and started from scratch.
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7900X3D, 64Gb Corsair 6000Mhz, Gigabyte Aorus RTX 4080 Super, Samsung 980 Pro 2Tb NVME
Unraid Server, 130TB Supermicro CSE-846, AMD Epyc 7551P 32 Core, 64Gb ECC DDR4, nVidia RTX A2000