I have an older computer as back up and rarely use. But I was wondering if someone could help?

Basically, I have a monitor set up via HDMI and an old AMD 5860 graphics card. And no videos on YouTube or Sports apps will play. They constantly come up with an error and either stop straight away, or not play period. I thought it was an AMD issue and reinstalled a beta driver and it worked and no sound. That's because HDMI was selected for my default sound when I use an Audigy card after the driver install. However, when I changed back to my Audigy the videos no longer play again and come up with an error! Any idea how to get them to play using my Audigy soundcard setting? Don't understand why the videos don't play just because I haven't selected the HDMI playback option. My newer computer works both ways. With HDMI going into TV, and normal sound card and speakers.