I came back from a trip, turned on my iMac, only to see a black screen with a DOS-like prompt: "No bootable device -- insert boot disk and press any key."

It did not seem likely that the hard drive had already died, but I thought perhaps it was getting confused because I had a lot of USB and firewire devices plugged in. I pulled all the plugs and cables and restarted. Same error! I then tried restarting with the Leopard install CD in the slot, but got the same message.

It turned out that when I had re-imaged my Acer computer last week, using the restore DVD, I had changed the "Startup Disk" settings to the DVD drive. Seems like it USED to be the case that if you switched the startup disk to the CD/DVD drive, then started up again with no disk in the drive, it would revert to the main hard drive, but apparently this is no longer the case. Instead you get the ugly error message. Not even a sad mac face or an empty folder icon.

I further complicated the issue by having pulled the USB cable for the keyboard when I pulled all the others, and could not figure out why holding down the Option key did nothing! However this was soon sorted out, and holding down the Option key did allow selection of the main system drive. As soon as the computer rebooted, it was possible to select System Preferences: Startup Disk: Mac HD, and all was well again.