Your machine can't find a valid operating system. This can be caused by a corrupted system folder or a failed hard drive. Boot from the original system CD holding down the "C" key and start to install a system, the second screen the pull down menu appears. Go to Utilities. Open "Disk Utility" and see if you can repair the drive. If you can see the drive and disk utilities doesn't fix it then try installing a new system. If you can't see the drive then you probably need to replace it.