The problem is that anytime the iMac goes to sleep, it can't be awakened (forcing a cold shut-down). If the energy saver settings are turned off and you don't allow the hard drive to shut down (just the video), there's no problem. Also, on occasion, when you go to start up the computer it will show the start-up light but then stop with a black screen and flashing cursor. Forcing it off and trying again a couple of times manages to get by this. The iMac was taken to an Apple store where they ran an extensive diagnostic (beyond what the default OS provided diagnostic does). They did not find any hardware problems. However, when attempting to awaken the computer from sleep, it was reported that the CPU was not receiving a signal to awaken. They suspected it might be the power supply or a component on the motherboard. As a measure to rule out software as the culprit, they completely re-installed OSX 10.6.8 but that did not make any difference. So, it seems like this is a hardware issue of some kind, unless there's something the Apple folks missed. It's an old computer and they'd just assume replace the motherboard--but that's prohibitively expensive to do, relative to the cost of a replacement computer. Any ideas on what might be causing this inability to awaken the computer?