Hello madi281,
Welcome to the HP Forums!
I understand that the sound is low on your notebook. Can you please confirm whether or not the issue occurred immediately after the 8.1 upgrade or not?
In addition, please try the following solution:
1. Go into Device Manager. Click on Sound, video and game controllers.
2. Right click on the audio driver, and select Uninstall. Do not restart the computer.
3. The next step is to download and install the latest driver. For information on this, please look at this document for Downloading or Updating Software and Drivers for HP Computers.
Please let me know how it goes. Thanks!
Mario