Compaq 239158-999 - Mini Tower - Power Supply 250 Watt Hardware Reference Manual page 30

Hardware Upgrades
2-12
Removing or Installing an Expansion Card
When you install an expansion card, make sure you press firmly on
the card so that the whole connector seats properly in the expansion
card slot.
13. Replace the screw at the side of the expansion slot.
14. Connect external cables to the installed card, if needed. Connect
internal cables to the system board, if needed.
15. Replace the computer access panel.
16. Reconfigure the computer, if necessary.
Hardware Reference Guide