HI mickep:
Welcome to the forum! Thank you for your inquiry. I am pleased to assist you the best I can!
I understand that after upgrading to Windows 8.1 a couple of weeks ago, you have not sound. and a power error in device manager. It sounds like it is a hardware issue. I would run the "HP PC Hardware Diagnostics UEFI" click here. For your convenience I am also including the "Maintenance and Service guide for your computer. click here. Please note on pages 86 and 87, the spare parts number for a replacement card. Please let me know if you require further assistance.