Dell Dimension 2100 System Reference Manual page 55

To remove the 3.5-inch floppy drive from the lower bay:
1.
Remove the front panel
2.
Rotate the power supply
3. While holding the power supply, place the computer in the upright
position.
4. Disconnect the power and interface cables from the back of the floppy
drive.
5. Press the two drive-release rail tabs, and slide the drive out of the drive
bay.
Before you install the new drive, install the drive-release rails on the sides of
the replacement floppy drive.
5.25-Inch Drive
1 Drive-release rail tabs (2)
.
away from the system board.