From your description:
It's not the power supplies (assuming they have enough power to handle your video card)
It's not the video cards
It's not the monitors
What you want to do whenever you troubleshoot, is work your system down (some prefer to work their way up), to (from), the lowest possible system required:
mobo w/cpu and heatsink, psu, video, monitor, keyboard, mouse, boot drive, and NOTHING ELSE.
no fan controllers, no external speakers, (beeps from boot up errors are on internal "mini-speaker", anyway), no other drives, no other pci boards, and no front panel connections.
Start is made by a short with a small screwdriver, across the pins of the front panel connector on the mobo.
You've finally come quite close to this methodology, but keep the above in mind if it should be needed in the future. You need a logical step by step approach, and no extra parts can get skipped.
Without another mobo or cpu to swap in/out, and without more detailed data, it isn't possible to know what is wrong, with your system.
Try to disassociate how you feel, from the problem. Take the troubleshooting steps slowly and carefully. Never rush through it - that's THE biggest problem with those unfamiliar with it.
Many times when a mobo goes "dead", there is no beeps on boot up, because the beeping is no longer possible - the boot up process never gets that far. Sometimes the board problem will destroy the cpu, sometimes it won't. There is no way to know for the end user, except by a swap into a known good, and compatible, system.
Overall, you've done a good job here. The fan controller should have been disconnected earlier on, but there is always a learning curve in troubleshooting a PC.
I'm not an admin here, but I've built up a LOT of computers. I have 7 of them in my home currently, 3 x 1 cpu, 1 x 2 cpu and 1 x 4 cpu system. I've followed your thread from early on, and you've been given good advice.
Good luck with your further work on this.
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