Desktop Audio

I recently purchased a refurbished HP Elite 8300 SFF with Windows 10 64 bit. After setting it up, everything worked except for audio. It has Realtek onboard audio (High Definition), and everything looked good in Device Manager (two entries), but Windows showed the red "X" next to the speaker in the lower right system tray. When I try to open it up, it tells me there is no output device available. I tried multiple drivers, uninstalled and reinstalled, but same thing each time. I finally gave up on the onboard audio and bought a Sound Blaster Audigy Fx PCIe card. I disabled the onboard audio in the BIOS and installed the sound card. I downloaded the most recent Windows 10 drivers from Creative Labs and again, it looked good in device manager, but also, again, I got the exact same problem -- red X and no output device available. I have tried plugging and unplugging speakers and headphones into the jack, but no luck. I did get Windows to tell me I connected headphones into the front jack when I was trying the onboard audio, but nothing with the card. I am a Computer Science teacher with a degree in Computer Science. I worked as an IT tech for 14 years and have repaired computers, built computers, and have done a ton of troubleshooting -- this one has me stumped and it is VERY frustrating!

I even contacted Creative Labs tech support and they could not solve it -- they are going to "get back to me through email" -- I'm not holding my breath...

Any help would be greatly appreciated.

Thanks.