Headphones help please .... Windows 10

I have headphones that work perfectly on bluetooth from my laptop but if/when the battery goes flat in the phones I connect them to the pc with a cable. This should also work perfectly, and has done in the past.
However now it just gives a very poor scratchy sound. no quality at all.
I've connected them to my phone with the cable and it works fine so the cable would appear to be ok.
Any ideas what may be causing this?
There's no change if I jiggle the jack plug in the pc, no odd noises, so I don't think it is the jack socket.
Ta.

 

Look down at the right hand corner of your screen next to the time & date , locate the speaker icon & click it , this will show you the current audio playback device , click the up arrow to expand your choices , select which ever one plays audio through your headphones
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Try putting them in your ears.