I am now sure that it's a technique problem but I have a capo on the second fret and trying to do hammers on the A and D strings on the fourth fret. The D is fine but the A is dead. I've done this on all three of the guitars sitting here and it happens to them all. It has to be my technique. Not sure what I'm doing wrong.

Any ideas? It's not the greatest capo, just a cheap one. (Yes, a cheapo capo...hmmm, that's odd). Any help would be appreciated.