When I booted up my iMac yesterday, I was confused to find my login field had seemingly moved upwards, so that only the bottom half was showing. The lower half of the screen was just black. Is this a screen calibration problem? The display corrects itself once I log in to show a normal desktop. I've tried rebooting.
Reference:
iMac 27", Late 2013
Running OS X El Capitan v.10.11.2
Screenshot of the problem is attached below:
Best Answer
I'd start with the standard "troubleshooting toolkit" ...
do all, in this order.
Reset the SMC (instructions depend on Mac model)
Reset the NVRAM
Verify & if necessary Repair disk, using Disk Utility.
Fix permissions.
Before El Capitan this could also be done from Disk Utility, now it needs to be done from Terminal.
Verify permissions
sudo /usr/libexec/repair_packages --verify --standard-pkgs /
Repair permissions
sudo /usr/libexec/repair_packages --repair --standard-pkgs --volume /
Reset Home folder permissions & ACLs
This has also become more complex since El Capitan because of System Integrity Protection, but is still possible by booting to Recovery Mode...
resetpassword
and hit Return\Enter. A Reset Password window opens.Start in Safe Mode
Update to - or if already installed, then re-apply - the latest available combo updater for your current OS, not the usual delta update from App Store.
Note: You can always search the latest combo update at http://www.apple.com/us/search/os-x-combo-update?src=serp & hone further by adding the version you're looking for in the search box at the top.