OK! I hate ridiculous solutions, but this actually seems to work!
My displayport of Macbook Pro 2011 edition stopped working ... suddenly!
I tried a lot of restarts, plug-ins and plug-outs .... and the usual tinkering.
I thought it was a cable problem and plugged it into my Macbook Air and the dislay worked just fine!
I searched a lot till I found this and this answer!
The following solution worked like magic .. for now!
Boot up normally... make sure your monitor is already set to the right video (ie dvi, hdmi etc) Unplug the monitor Power cable, then plug in your cable (ie mine is DVI) to your macbook, (the screen should go blue for a sec.) Then, only then once your screen comes back, plug in the power cable to the monitor. Somehow it resets mine everytime, and my macbook redectects the monitor. So rediculous, that I also as a graphic designer (which ive seen a few on here) who need their **** externals are dealing with this. Really hopes this saves someone the pain i've went through on this.
OK! Now if this doesn't work ... Try to Reset PRAM and SMC
Those are all my options and they seem to work after a few tries! Good god!
