Took the iMac down to the Apple Store at the Galleria today, and if their hardware guy hadn’t been out to lunch, I could have had it fixed while I waited. The guy at the Genius Bar (Eric) suspected it’s just a bad power supply. He said that I’ll probably have it back this evening or tomorrow.
Update: The Apple Store just called (7:10pm) and it’s fixed. I’ll pick it up tomorrow.