Cause 1: Your computer located the system software on your hard disk before it located the system software on the CD. If you have an external hard disk with system software, the computer may locate and start up from that device instead of the CD.
Solution 1: With the CD inserted, open the Startup Disk control panel and click the CD icon in the Startup Disk window. Then restart the computer.
After you install the software, use the Startup Disk control panel to reselect your hard disk, then restart your computer.
Cause 2: You don't have an Apple-brand CD-ROM drive, or you're accessing the CD from a PowerBook using file sharing.
Solution 2: To ensure a smooth installation, turn off any disk security or virus-protection software you have installed. Then follow the steps in this section to temporarily disable all non-Apple extensions and control panels so they won't cause problems during installation.
If you are using System 7.5 or later, use the Extensions Manager control panel to turn off non-Apple extensions and control panels. In the Extensions Manager, open the Sets pop-up menu and choose the item that has the word "base" and the version of system software currently installed on your computer. (If you have System 7.5, choose the item that has "system" in it.) Then restart the computer.
If you are using an earlier version of system software, or don't have the Extensions Manager, do the following:
1. Open the System Folder, then open the Extensions folder.
2. Drag any non-Apple extensions out of the Extensions folder and onto the desktop. If you don't know where a particular extension came from, click it once to select it, then open the File menu and choose Get Info. If the Version section of the Info window doesn't say "Apple Computer, Inc.," drag the extension to the desktop.
3. Open the Control Panels folder.
4. Drag any non-Apple control panels out of the Control Panels folder and onto the desktop. As in step 2, use the Get Info command if you're not sure whether to remove a control panel.
5. Restart your computer.
After you've finished installing the software, you can drag the extensions and control panels back to your System Folder. To make sure the software is compatible with this version of the Mac OS, restart your computer after you reinstall each item.