I just received my new 20" base iMac last night, and I am having some issues with the sleep mode. Twice, when trying to wake it out of sleep all I get is a black screen. I see the monitor light up and hear the hard drive spin. I even get the "ding" sound when I press keys on the keyboard, but nothing else happens. As a switcher from the dark side (Windows), this is my first Mac. Here are the 2 situations when this happened: 1. The first time I turned on the computer. No external devices attached except the wired keyboard and the Apple mouse plugged into the keyboard. I walked away for about 20 mins during the setup process when you first boot a mac. When I came back, it was asleep and would not wake. 2. This morning. No devices attached except wired keyboard and Microsoft mouse hooked into the keyboard. I have installed HP's printer driver, Microsoft's Wheel Mouse driver (the Apple mouse does not track properly on my surface) and I migrated pictures and music from my Windows laptop via a USB drive. I did not make other changes or install new programs. Before I put the computer to sleep, all applications were working fine. No third party stuff was running. I had used the menu command to put the Mac to sleep. All OS updates have been installed. Both of these times, I have had to hold the power button until the machine shuts off. In Energy Saver, both the computer and monitor are designed to sleep after approximately 10 minutes. An interesting thing is that I put the Mac to sleep a couple of times yesterday and it woke up just fine. However, the computer was only asleep for a few minutes. I will try to look into this more after I get home from work today. Does anyone have any ideas? If you need more info, please let me know.