Dell OptiPlex 330 User Manual page 208

Snap the cover into place by pulling back on the cover release latch
c
and then releasing the latch when the cover is properly seated.
Ensure that the cover is seated correctly before moving the computer.
d
4 Move the computer to the upright position.
NOTICE:
and then plug it into the computer.
NOTICE:
5 Connect your computer and devices to an electrical outlet, and turn
them on.
208
Mini Tower Computer Parts
To connect a network cable, first plug the cable into the network device
Ensure that none of the air-vents of the system are blocked.