Yeah, try another monitor. I don't think that your hardware is failing as much as there might be a compatibility issue. But even if that was true, your onboard stuff still would work. If I were you, I'd hold off a little bit on getting another motherboard, because that would be the second one you would have gotten, yeah?
And how many non-onboard video cards have you tried? Also, list everything that you have (on the new board) that was the same from the old board. And while your at it, make sure the little jumpers on your board are all the way down, because my friend had an intresting problem with that in the past.
EDIT: Also, was your old motherboard the same type as the new one you got?