I don't know what the problem is at this point. The MacBook will output to a 17" LCD I have, but not to the 20" LCD I have always used with it. The Mac mini, on the other hand, has no issue with outputting to either, using the same cable. I had the adapter tested at the local Apple store, because I had thought the adapter was bad, but they let me test my MacBook and adapter with an Apple display at the store and it worked without a hitch. When I cut or give power to the 20" LCD with the DVI cable plugged in, the MacBook's screen will go blue for a few seconds as it always does when it connects or disconnects to an external display, but afterward does not even acknowledge it, and the 20' LCD remains blank. Again, the 20" LCD and the 17" LCD will work with the Mac mini, using the same DVI cable, and the MacBook will work with the 17" LCD and the Apple Store display using the same DVI cable and its own adapter, but the MacBook will not will not work with the 20" LCD. I have replicated my experiments with two different DVI cables, one a DVI-D Dual Link and another a DVI-D Single Link, with the same result. What is going on here?