Apple Power Macintosh 8500/120 Series - Manual (Page 165)

11 Replace the cover on the computer.
Lower the cover all the way down onto the case. Push the cover back until it
touches the back panel.
12 Tighten the screws on the back panel.
You may now turn on the computer and use its expanded capabilities.
WARNING Never turn on your computer unless all of its internal and
external parts are in place. Operating the computer when it is open or
missing parts can be dangerous, and can damage your computer.
153 Installing an Expansion Card