It's the same occasional problem I had on my old Compac PC - my Mac goes into sleep mode but won't awaken. It occurs about 1 out of 10 times that when I click the mouse to wake up my sleeping Mac that the monitor awakes from a black screen to display the cosmos desktop but nothing else (that is not my selected desktop when the Mac is working). No dock icons display and no sound of the hard drive coming to life. The only way to get it out of its coma is to depress the on/off button until it shuts down - wait 10 seconds and then restart. Is this a common problem in both PCs and Macs?