I had HDD drive cable in backward causing this kind of problem at boot with ASUS Mobo. It had on board graphics and I was using a PCI card for video. It was working great until I moved the HDDs to make room for airflow. That is when I got the cable on 1 HDD backwards. No beep, no video, I can't remember if the HDD had spinup, but like you I figured I lost the CPU or Mobo. So maybe try booting no HDD connected. If it comes up then well you go from there.
I have hooked 2 wire fan on Mobo with 3 pin wire connection but it fried up, no problem. If this were the case the manual would have a note saying so. You should take a look in manual.
No video at all may have to do with the BIOS but you have onboard graphics so not likely, but if you have an AGP card that you know works try putting it in. IF the video comes up with an AGP card in place see if the onboard graphics is turned off by/in the BIOS.

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