New mobo - comp still won't boot

The computer isn't much better than last time. I'm running an Asus
A7V8X-X mobo. As soon as I flip the power switch on the ATX PS, the
whole thing turns on (fans start spinning, etc.), which is bad, because
usually the computer waits for me to press the power switch before
turning on. I've reseated the mobo, re-checking the metal stand-offs.
Those are fine. I've reseated the CPU, heatsink, video card, and
memory. Still, nothing at all happens - it doesn't post, and it never
sends a signal to the monitor. I know the CPU works, and the RAM and
mobo are both new. Any clue as to why this computer won't boot at all?
Why it doesn't even recognize the power switch and just goes full-on
immediately? Thanks in advance for the help.

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