Last week we reported that users of Macs Pro were experiencing graphics card issues after upgrading OS X Mavericks to version 10.9.3. But this doesn’t seem to be the only one.
In some topics (1, 2) in the Apple discussion forum (Apple Support Communities), users complain that updating the system has somehow disabled the use of multiple monitors. Those who worked with four are now able to use only three; others that had three monitors connected to the Mac Pro can now only work with two.
Some managed to remedy the situation by reinstalling the version Combo OS X 10.9.3 (available for download from the Apple website); others said that a PRAM reset will do; lastly, a user stated that reinstalling the GPU drivers used in OS X 10.9.2 is also a good option.
Let's hope that all this will be resolved by Apple soon, who knows with the arrival of OS X Mavericks 10.9.4.