Here's the exact link for your product at HP Support Site -
Software & Drivers
I have a few suggestions for you to consider;
1. Please use the official build 7000, if possible.
2. From the download list, upgrade your BIOS first
3. Download the audio
driver
4. Uninstall the current audio driver
5. Install the downloaded driver
6. Restart
Now, if the above steps still doesn't get your sound going, check this post -
Windows 7 Driver solution
Let us know how it turns out