It appears HP has Vista drivers, but not Win 7 drivers. If you need, you might be able to get the Vista drivers to work. Have you right clicked on the speaker icon and checked the settings for the Playback and Recording devices? What do you show as default devices?
If you have this info already, please post, but you may need to go to the HP site and put in your specific information to get detailed information about your system. The chipset being used and the audio would be helpful. Is it Realtek audio or something else. Is the chipset and Intel 815 or 830, or what.
I suppose the bottom line is that if your current install is not sufficient for you, additional drivers may be needed. Windows will, in some circumstances, update drivers...