Dell Dimension 2100 System Reference Manual page 52

To remove the front panel:
1.
Remove the computer cover
2. While facing the front of the computer, press in the front-panel release
tab the top of the computer.
3. Swing the front panel away from the computer, disengage the two
retaining hooks at the bottom of the front panel, and carefully pull it
away from the computer.
4. To replace the front panel, fit the two front-panel retaining hooks into
their corresponding slots on the computer frame. Rotate the front panel
toward the computer until the front panel latches into position.
.
1 Front-panel release tab
2 Retaining hooks