HP Compaq Pro 4300 Small Form Factor Reference Manual page 27

9. Before installing an expansion card, remove the expansion slot cover or the existing expansion
card.
a. If you are installing an expansion card in a vacant socket, remove the appropriate
expansion slot cover on the back of the chassis. Pull the slot cover straight up then away
from the inside of the chassis.
Figure 2-12 Removing an Expansion Slot Cover
Removing or Installing an Expansion Card 21