3. Installing the FireWire® 800 PCI Card
Step. 1
Shut down your computer
• In Mac OS X, choose Shut Down from the Apple menu.
Warning! - Always shut down your Power Mac G4 before opening it to avoid damaging its internal components or the components you want to install. Do not open the computer or attempt to install items inside it while it is turned on. After shutting down your computer, the internal components can be very hot. Let the computer cool down before continuing.
Step. 2
Wait five to ten minutes to allow the computer's internal components to cool.
Step. 3 
Unplug all the cables from the computer, except the power cord.
Step. 4
Lift the latch on the side of your PowerMac.