ive experienced this problem before and the no signal on the monitor has nothing to do with the video card.
now if i read right and you fired up your board missing one of the 12v 4 pin plugs then your computer did not power on to save your hardware.
most likely due to your first power on not working your board is now not reading your cpu/ram. or it may have fried the ram.
first thing i would do is try sticking your ram in another computer one stick at a time and booting to ensure it all works fine.
then reseat your cpu, cleaning off the old TIM and remounting the HSF. check the pins on your cpu also.
i recently bought a water cooling system that rendered the same exact problems after i installed it. all fans and hardware would turn on, but the computer would not post, and it read a "no signal" message on the crt monitor i was using. tried a new mobo and everything!
turns out it was a faulty mounting bracket for the cpu block causing my mobo not to read the cpu. put the stock HSF on and reseated the cpu, it fired right up with no problems.
other than that its replace parts time.....