Hi Laptop2..
Welcome to the forum! Thank you for your query. I will do my best to aid in this endeavor!
I understand that after updating to Windows 8.1, you are having an issue with the HDMI feature. You can run the Windows built in troubleshooter, to aid in looking for updates( Window key +c to open charms, type troubleshoot in the search bar). You may need to check the manufactures website for an updated driver, as was stated in the previous posts. Here is a document on "Downloading or Updating Software and Drivers for HP Computers"click here. Here are links to "Troubleshooting Sound Issues with HDMI" click here, and "Overview of Switchable Graphics or Dual GPUs" click here. Please feel free to reply, if this has not resolved the issue.