HP Compaq dx6120 ST Hardware Reference Manual page 22

Hardware Upgrades
2-12
To install an expansion card:
1. Turn off the computer properly through the operating system,
then turn off any external devices.
2. Disconnect the power cord from the power outlet and disconnect
any external devices.
3. Remove the computer from the stand and lay the computer on its
side.
4. Remove the computer cover. Refer to
Cover."
5. Identify the slot into which you want to insert the expansion card.
6. Release the slot cover retention latch that secures the PCI slot
covers by lifting the green tab on the latch and rotating the latch
to the open position 1.
7. Remove the slot cover by sliding it up and out 2.
Removing the Expansion Slot Cover
www.hp.com
"Removing the Computer
Hardware Reference Guide