Please do try these troubleshooting steps that may help in resolving the issue.
- Do try to uninstall/reinstall the sound card driver first.
- If your sound card is not listed in Device Manager try to download and install the latest driver there is from HP support site.
- Here's the link: http/support.hp.com/us-en/drivers/
- Just click on "Identify now" so it would give you the exact driver you need for your laptop.
- Once installed reboot your laptop and see if you'll have sound back.
- If these will will not work try performing System Restore, restore it back to an earlier date or time when everything was working properly.
- If System Restore will not work I would suggest running a complete factory reset first before contacting HP support if it's still is covered by their factory warranty.