Did I kill the pixels on my monitor?

Help! I think I may have mucked up my external monitor! I have a 4K Seiki television that I’m using as a monitor for my MacBook Pro, running Mavericks. While fiddling around, I changed the Display Preferences to 1080p on the monitor and now I can’t get out of it! My only options are 1080p and 720p. I’ve tried reinstalling OS X, doing a factory reset on the TV and resetting the PRAM. Could I have physically damaged the TV by running the wrong resolution? James Grafton No. I think you’ve just turned off HiDPI mode. This is the doubleresolution that Retina displays use; 4K televisions work the same way. Once you’ve switched off HiDPI mode, Display Preferences shows only the ordinary low resolutions. You may find that you get the Retina resolutions back in Safe Mode though, so it’s worth trying. Otherwise, you can force HiDPI back on via Terminal: sudo defaults write /Library/Preferences/ com.apple.windowserver.plist DisplayResolutionEnabled -bool true Restart after you’ve entered it. If you find yourself doing this a lot, try an app called ResolutionTab on the App Store for £1.49. It lets you do it via a menu bar icon.