Dell Precision 330 - Manual (Page 11)

Replacing the Cover (Desktop Chassis)
Mini Tower Chassis
l Removing the computer cover
l Replacing the computer cover
Removing the Computer Cover (Mini Tower Chassis)
1. Turn off the computer and peripherals, and disconnect them from their electrical outlets.
2. If installed, remove the padlock from the padlock ring on the back panel.
3. Remove the computer cover.
a. Face the back of the computer and slide the outer padlock ring to the left to unlock the cover release mechanism (see the following figure).
Cover Release Mechanism (Mini Tower Chassis)
CAUTION: Before you perform this procedure, see " Precautionary Measures ."