I've been editing on an iMac running OSX 10.9.5 for over a year. I have an LG TV serving as secondary display, going through a Samsung sound bar. Never had a problem with it.
This week, my office moved and when I plugged everything back in, I found out that whenever the TV was turned on, the computer would have major bugs. FCP 7 and After Effects won't open, they just stall. I can't force quit anything, when I press the buttons, the force quit window just doesn't appear. I can't reboot or shut down the computer or open System Preferences. At this point, the only thing I can do is shut down the computer manually.
When the TV isn't turned on, everything still works fine, though. I tried trashing preferences, repairing disk permissions, but nothing works. Anyone ever saw anything like this?