Apple IIgs help

Would it be correct to assume that an appropriate boot diskette is in place? Have you tried another boot disk (sometimes, old diskettes lose data)? Alternatively, do you have access to another disk drive? Additional information about peripherals and installed cards?

That means you don't have a viable boot disk in the disk drive. In order to start up without a disk in the drive - just hold down the Ctrl key and tap the reset key. The locations of the reset key will differ a bit depending on your keyboard - it may be the odd, rectangular-looking bar/key above all the rest on the keyboard. Once you successfully reset the machine, you'll be faced with an Applesoft prompt (a right brace, "]") and you will be able to do some BASIC programming (without a means of saving anything on disk).