My late 2009 iMac started developing a weird issue. I've noticed during the last week or so, the display will not sleep. To give you a bit of background, the machine was recently reinstalled with a fresh OS X 10.8.3 installation about 3 weeks ago. I'm not sure if it's related to 10.8.4, as none of the other various configurations of Macs are being affected. I've tried putting the display to sleep @ 1 min, and it doesn't go to sleep. I went into the desktop & screen saver preference and setup a hot corner to make the display go to sleep. The hot corner puts the display to sleep, but after 10-20 secs (it varies), the display comes back on. I've tried closing down all app until nothing is running, but the display keeps waking up from sleep. Has anyone experienced this and has a solution? I'm going to try installed 10.8.3 from scratch again, then restore from time machine to see if it'll fix it. Not the best solution, but don't think I have any other option unless someone else can help. Thanks in advance.