Today after using the external ViewSonic VX2025wm display with another computer and replugging it to my MacBook, suddenly it did not get recognized. Just as described here the internal display goes blue for a sec and then returns to desktop just by itself.
First I was afraid that I had hurt the monitor somehow (damaged the pins or killed the electronics with statics), but plugging it back to the other computer cleared that road.
Next I checked the VGA input of the same monitor with the MacBook – everything worked fine. So my book still has ability to detect external monitors. Next thought: DVI output or Mini-DVI to DVI adapter. When I plugged in another monitor with DVI all worked. Last reort – the DVI cable, though hopeless as it was working with the other computer. Replaced the cable, but to avail – MacBook still did not detect my DVI input. And no, reboot did not help either.
This left me clueless. I have a working monitor and working MacBook that do not detect themselves but otherwise work just well.
Searching through the net, several posts, including the one linked above, mentioned that as a last resort, one can reset the PRAM on their Mac. But I was reluctant to do that, so I dug more and found this post had another option that was reported working partially.
Unplug the monitor power cable
Unplug all cables and detach the power cable from the monitor. Leave the monitor like this for 1-2 minutes and if you are as lucky as I was, replugging cables should return you to your external DVI display.
It sounds ridiculous, but it seems that the monitor held some kind of grudge against my MacBook that got cleared with the power outage. What kind of gremlins live inside our devices!?