First try if it works when you boot from a Linux disk or stick (easy to make and free).
Then, if it doesn't work there either, have it repaired under warranty (free also).
If it works in Linux and not in Windows, restore back to factory conditions and it should work again.
i have a laptop that is new and working fine until today.
i have sound coming out of speakers but not on the phones.
when i plug phone jack i see the icon change. Headphone is detected. i see green light activity showing sound should be going to headphone but i hear nothing.
Headphones are ok (tested on something else)
i tried with other computer
here is a picture of how it looks :