Dell OptiPlex 360 (Late 2008) - Manual (Page 17)

Before Working on Your Computer 17
After Working on Your Computer
After you have completed any replacement procedures, ensure you connect
any external devices, cards, cables, and so on before turning on your
computer.
1 Replace the computer cover (see "Replacing the Mini Tower Computer
Cover" on page 21).
2 Connect any telephone or network cables to your computer.
CAUTION: To connect a network cable, first plug the cable into the network
device and then plug it into the computer.
3 Connect your computer and all attached devices to their electrical outlets.
4 Turn on your computer.