I'm stumped on this and hoping someone has a tip. Bought two mini displayport to DVI adapters and cables for two macbook pro 13" mid 2012 laptops. So I have two of everything to be able to swap adapters, cables, even macbooks. Can't get it working. The macs "see" the external monitor when I go into Displays, and will let me drag it around in the "Arrangement" tab. But the external monitors both say "No Signal" on DVI input. Running Mavericks. Any tips? Did I buy the wrong adapters? Any help appreciated!