Dell Dimension 2100 System Reference Manual page 49

To remove the computer cover, perform the following steps.
NOTICE: To avoid inadvertently damaging the system board, be sure you that
disconnect the computer from the electrical outlet, disconnect the power cable
from the back of the computer, and press the power button before removing the
computer cover. This computer continues to receive a small amount of power
when the computer is turned off and attached to an electrical outlet (the system-
board power light
1. Face the front of the computer. Place your left hand on the left side of
the computer. Push back the release latch at the top back edge of the
computer to release the computer cover into your left hand.
2. Lift the cover out from the curved hinge at the bottom of the computer.
CAUTION: Keep your hands clear of the metal edges on the computer
frame and fan guard as you slide the cover back.
To replace the computer cover:
is on when power is detected).
1 Release latch
2 Computer cover