If you received your Windows 7 upgrade from HP, run the Upgrade Assistant disk that came with it. This should install all your software, including your sound driver, for use in Windows 7.
If you purchased the Windows 7 upgrade separately, you should be able to find the sound driver for your computer on HP's website. Go to www.hp.ca then their Support page. Type in your computer's model number when prompted, then select your version of Windows 7 from the list. You should be able to locate, download, and install your soundcard's driver software from there.
Let us know how the above worked. If you aren't missing your driver software (or if it isn't working despite installing it) then we'll need to figure out what else may be the issue.
Hope that helps!
