I have my iMac set to sleep after 15 minutes, both monitor and computer. I also have it set to "Put hard drives to sleep when possible". Sometimes when I come back to my iMac I could bump the mouse and it will immediately turn back on. Other times bumping the mouse does nothing so I hit Enter and the computer makes a noise (I believe it's checking the CD-ROM) and then wakes up after 3-4 seconds. I can't find the reason why it does two different things. I only really run Safari and when I leave the computer I minimize it, that's the way I always leave the computer when I leave it. Sometimes I'll come back after 30 minutes and have to wake it up with the keyboard. Other times I'll come back after 12 hours and just bumping the mouse will turn the screen back on. Anyone know what's going on? Thanks!