Cannot get onboard audio to work. Help?

Today I built a comp with a "ASUS M3A78-EM AMD 780G HDMI" mobo in it. I cannot get sound from the ports in the rear. I have installed the drivers from the disk that came with the motherboard, which included the "Realtek Audio Drivers" and "ATI HDMI drivers". I am using speakers, which I know work, and have them plugged into the lime green port on the rear, seen in this pic. I have also tried all the other ports, just to make sure, while a song was playing. The computer is not saying that there are any issues anywhere. I have gone and also uninstalled the Realtek drivers and installed the latest that their site provided. This didn't do anything, so I've reverted to the ones on the disk. I am not using anything special; just simply using two speakers plugged into the rear port. Can anyone help?

Also, shouldn't the motherboard ports for sound work right away? As in, you can't have a funky wiring issue like you would have if you were trying to connect speakers or headphones to the jacks in the front of the case (which require a little wiring).

What speakers do you have and are they plugged into power supply

I am using that board with a computer I just built this weekend.

Right click on the sound Icon on the taskbar (near the time) and click on playback devices to see which output it is using by default.

When I first set up the OS, the system set itself up for digital out.
I just changed the setting by enabling speaker out and it worked fine after that.

Good luck.