have you checked all the power cords plugged into the motherboard? there is a possibility that one of them might not be properly clipped in anymore. also, did you make sure the CPU cooler is still properly seated? try unplugging the hard drive also. it cant hurt, and as you said, you should still be able to post.
one way to see if it is really the motherboard is to turn it on, let it run for a while, then feel the northbridge/south bridge heat sink. if they are not warm, then something is wrong with the motherboard. if they are warm, then i am not entirely sure right now what the problem is.
one way to see if it is really the motherboard is to turn it on, let it run for a while, then feel the northbridge/south bridge heat sink. if they are not warm, then something is wrong with the motherboard. if they are warm, then i am not entirely sure right now what the problem is.