Lost All sound from Dell 17XPS

I have had a Dell 17XPS for around 18months and am delighted with it. All of a sudden yesterday, I lost all audio. Going into settings , settings, system. I see the message.."No Audio device found" Not even the sound card installed by Dell. I have deleted all the sound drivers and reloaded the correct ones from the Dell Website but still no audio. BUT, if I use Bluetooth headphones I get audio just fine (which is very confusing). I am 72 and having worked in Broadcast TV in the UK I was a bit like Indianna Jones and the closing door.... I just made it as far as computer literacy is concerned and built my own PC, a Nascom 1 in 1976! So I do understand systems etc. My biggest question is Why does my machine not see the sound card that coes with the machine. It MUST be there because it works on Bluetooth. Any help suggestions much appreciated.