I have a macbook in clamshell mode that's plugged into an HDTV for display output. Yesterday, I changed my display settings via the System Preferences. However, I inadvertently picked a setting that is not supported by my screen, and now I can't figure out how to undo the change. The screen is blank.
I can open my laptop and go to dual-screen mode and change the settings there, but as soon as I switch back to clamshell mode the system picks the broken display settings again.