Last night I was away from my computer for a few hours and when I got back to it, the screen saver was still running. The display didn't turn off after 20 minutes and my iMac didn't go to sleep after 3 hours. I think I was away from it for 4 hours or about that. I have a 20" 2.4 Ghz iMac. I'm aware that the "don't dim the screen before sleep" doesn't work right. Is this related? The strange thing is that it's worked properly before.