From all your symptoms you're giving and all the things you've tried, I am putting my money on the motherboard. I had previous systems with boards that gave boot up problems but was slightly different from yours. Usually if the Ram or CPU is bad, it would at least give beeps and/or be able to go to the Post screen showing the errors. Obviously resetting the Bios didn't help, which is the usual way to reset problems like this. As far as whether it's the Bios or something physical on the board, that's up for grabs.
Before attempting an RMA on the board, if you had the resources to test the CPU, you could do that before sending it off. I think I'd still attempt to RMA it and see if you can get a replacement and if you do get a replacement, I'd still sell it and go for an Asus board.
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