Then plug the power cord back in and press the Power button on the computer to turn it on.
If that doesn’t work, unplug the power cord from the computer.
When the computer turns off, press the Power button again to restart it.
Hold the Power button on the computer for five seconds.
If the computer still doesn’t respond, restart it, to do this: Hold down the Option and Command (x) keys, then press the Esc key.
Try to force problem applications to quit.
Then try to cancel what the computer is doing.
Unplug and then plug in the connectors and make sure they are secure.
First, make sure the mouse and keyboard are connected.
Select the Mac OS X System as your startup disk.
Click the triangle next to the hard disk that contains your operating system folders.
Choose Control Panels from the Apple menu.
To set the computer to use Mac OS X again: If the icons are dimmed, click the padlock icon and enter the password you chose when you first set up Mac OS X.
Now select the Mac OS 9 folder as your startup disk.
Then click the Startup Disk icon to open the Startup Disk pane.
Choose System Preferences from the Apple Menu menu in Mac OS X.
To set the iMac G4/700 SE (Flat Panel) computer to use Mac OS 9: You can also start up your computer using Mac OS 9. Just open the application as you normally would. Most applications made for Mac OS 9 will work in the Mac OS X Classic environment. How to Switch Between Mac OS X and Mac OS 9