I have a new 27 iMac i5 and Im experiencing an issue with it waking up from sleep mode. When I first received the machine a week ago I noticed several times that when I went to wake it up from sleep mode it wouldnt fully come up. The system fan would start up however the screen would stay black. I did a reformat\reload of the OS (10.6.2) and the problem went away (so I thought). Last night the machine once again did not wake up properly. I tried putting the machine back to sleep without success. Finally, I powered it off using the power button and turned it back on. I looked at the log files and there wasnt anything recorded in them about an unsuccessful wakeup from sleep or any messages at all during that time period. There was an error relating to an unexpected power failure (probably relating to it being turned off while sleep mode was engaged). The time stamp for this error was later around the same time the machine successfully booted up after I turned it off. I do not have any devices plugged into my machine or any software programs that should interfere with sleep mode. There is one thing that happened last night that might be related to this issue. I have a Brother Laser printer that dims the lights whenever I print. I used it last night while the iMac was asleep and I wonder if its related. Its never been an issue with my PCs or the 21.5 iMacs I had before I upgraded to this 27 iMac.