screen saver won't turn on
This started yesterday, as far as I can tell. I walked into my office and the display was on, unlocked, and just sitting there. It should have gone to the screen saver, and eventually put the display (but not the computer) to sleep. As far as I can tell, it is no longer doing either. I can set hot corners to get the screen saver to turn on or the display to sleep, but it won't do it on its own. I tried clearing the PRAM. After the reboot/PRAM clearing procedure I set the screen saver timer to 1 minute. It worked, but it hasn't worked again. I have a brand new 27" iMac running OSX 10.8.3. Everything is as up to date as possible. Any ideas?
Thanks,
Dave