My headphones are not getting detected

i have recently installed windows 7 one n half month back.....previously i couldn't hear the sound at a time from both headphones n speakers.
so if i want to hear through speakers i have enable speakers in sounds or else headphones in sounds.
But now i can hear the sound only from speakers but not from the headphones even though they are plugged in n working properly.....n also there is a new icon in sounds named Digital Audio(S/PDIF)
can u plz give instrutions how to make use of it n wht is its purpose.
Also plz solve my headphones problem

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