I have the new 21.5 imac- Everything is working fine, but I have it set to start the screensaver at 15 minutes. Every time I leave the house and come back, the computer screen is still on. No screensaver is evident. I even try to put it to sleep sometimes, and it will go to sleep and then wake up abruptly. Why is this happening? And is it bad to have the screensaver not work? Can it mess up my computer? I'm thinking about shutting off the machine when I'm not at home, but I have been advised that its better to put it to sleep.