I have a dell optiplex 9010 MT. on the front, theres 2 headphone jacks, one for audio and one for mic. on the back tho, theres 1 that has both symbols on it, so im guessing its a combo? but when i plug my headphones in, the sound doesnt come, only my mic works. iv installed the lastest realtek audio drivers but it still wont work, in sound devices it says speakers/headphones but i cant hear any audio