HI DaFencer:
Welcome to the forum! Thank you for your post. I will do my best to assist you!
I understand that after updating to Windows 8.1 your sound was fine until HP support assistant installed updates. Here is a document on "No Sound from Speakers (Windows 8)" click here. There are updated drivers for Windows 8.1 on the support and driver page. click here. Here is a document on "Switchable Graphics on Notebooks Configured with Intel and ATI GPUs" click here, If you require any additional help please do not hesitate to reply.