No signal to monitor, no beep, no bios, can't boot,

here is the deal:

when i turn on my PC nothing shows up on my monitor, i can't even get into the bios.,

what i have tried:
i tried a new video card, no success,
i tried another power supply, no success
i tried resetting the memory, the cpu, , no success
i have removed all harddrives, and ubs connections and pci cards,- no success
i have cleared the cmos by followring the clearing cms instructions for my motherboard, but nada.

i have left just the video card, one memory stick, but still i hear no beep and i don't see anything on the monitor.
i know the monitor works because it works on another pc i have.
i tried a different memory stick from another computer, but no success.
i call also tell you that the cpu fans turn on, the case fans turn on, bu tnothing.

im thinking its my mobo, but any other  suggestiosns would be appreciated.