hey
let me guide u through some steps , to just check the hardware is working properly

1-Right-Click my computer and then click properties.
2-The System Properties Dialogue box with the General tab is active appear. go to the Hardware tab.
3- Click the Device Manager.
4- Check if there is any yellow icon(exclamation mark) saying other device.
5- if u find this icon.. then you have to download the latest Audio driver on the Hp website.

it might also that u disabled the device from ur volume controller ..
OR
ur Sound is MUTE...