My SO and each have a MacBook Pro. Hers is vintage 2007-ish, so non-unibody but Core 2 Duo. Mine is from 2009. We also each have an Apple Cinema Display. Hers is the original Apple-Display-Connector 22" Apple Cinema Display, and mine is the 23" ADC Apple Cinema Display HD. Yes, the plastic one. Yes, they're both ancient. Yes, they both have the ADC-to-DVI power supply thingies from Apple. When I plug either of the two computers into my 23" display, they work fine together. When I plug my computer into the 22" display, they work fine together. (Damn nice picture, too.) When I plug my girlfriend's computer into the 22" display, it seems to have absolutely no idea that a display has been connected. No flash, no indication of any power-on on the monitor, temporary or otherwise. No lines in the system.log file. Literally no indication that it is plugged in at all. Here are the troubleshooting steps I have tried. Please give them a quick look before you tell me to (e.g.) zap the PRAM. * As noted above, I tried the 22" display with my laptop. Works fine. * As noted above, I tried the 23" display with her laptop. Works fine. * Tried plugging the display in while the laptop was off, then turning it on. * Tried plugging the display in while laptop was asleep, then waking it. * Tried plugging the display in while laptop was awake. * Tried pushing the display power button while it was plugged into her laptop. * Tried the 'detect displays' button in the System Preferences. * Tried zapping the PRAM * Tried resetting the power management unit. * Tried unplugging/replugging display power while connected to the laptop. * Tried swapping the two power adaptors. (When I swapped the two power supplies, the problem followed the monitor, not the power supply.) So yeah. Does anyone else find this one as weird as I do?