My iMac was working fine last night. I downloaded a few photos from my camera into iPhoto and started up a slideshow to show my family. I forgot about it and let it run all night. When we woke up this morning, the iMac was off and would not turn back on. I've unplug the cords and checked the power outlets to confirm power should be getting to the unit. The iMac will not do anything. Is there something I can do to it other than take it to an Apple Store to get it looked at?