This may add light to the situation...for grins, I took out the included GeForce GTX 745 and put it into another PC I had. Plugged it in with VGA...booted...no sound, on a different PC (Lenovo ThinkServer T140)...plugged in via HDMI and plugged speakers into monitor...bam...working...removed the GTX 745 card, plugged into the onboard VGA...no sound...no matter what I tried...something in that digital audio from the video card permanently kills onboard audio, somewhere in the settings...any clue how to fix that? (may need another subject for this)
Also of note, I did a clean install of Windows 8.1 on the Dell and onboard sound still not working...but what is equally frustrating is now my Lenovo has no sound, even when removing the GeForce card and removing all drivers and devices.