On my Mac there is a small button on the back of the stack which switches it off when all else fails. Mine's not the newest model, though so it may be slightly different in a newer version.

To sort out problems, you'll probably need to boot from the OS disc - put it into the CD drive, switch on the mac while holding down the C Key, I think.

If you've got a CD already stuck in a drive (most probable) you'll need a paperclip to eject the cd. again, there's a small pinhole just beside the cd tray where you can put in the straightened out paperclip!

Great fun, technology.

Margaret