Before installing Mac OS 8.5, you should start up your computer using the Mac OS 8.5 CD. This ensures that any incompatible extensions on your computer will not cause issues during installation. To start up your computer from the CD:
1. Insert the Mac OS 8.5 CD into the CD-ROM drive.
2. Shut down your computer.
3. Hold down the C key on your keyboard while turning on your computer. Keep holding the C key until you see the "Welcome to Mac OS" message.
Note: PowerBook 1400 systems require that you hold down the Command-Option-Shift-Delete keys together to boot from a CD.