Came back to view the thread and saw the OS at the top & did a facepalm, had forgotten the OS already.
Of the ones in the back, the green one is usually the correct port, though you can sometimes plug it into any one of the jacks if the autosensing software is installed (depending on audio codec chipset)
The first thing you should do is make sure the hardware is working ok. Go to your start button, open the menu and look for "computer". Right click on that and choose properties, then click the Device Manager option. From here, make sure that all of the devices in the device manager are showing a + next to them. If there are any with a - next to "Sound, Video and Game Controllers" then we need to look more closely at that.
If the Device Manager looks ok, go to your control panel, and look for the sounds option. Open the window and verify that your slider is turned up beyond the 0% hash mark and that mute isn't checked.