If you have no sound first check that the audio cable is plugged in all the way, this is found on the back of your computer. This is usually a green ended cable or you might notice the connector port is green as well. This is the same of connector plug that you used to use on your iPod.
Next, you will want to check in the bottom right corner of your screen, click on the speaker icon, and make sure your audio is not muted. While you are there you can also check that you are on the correct audio source, to do this click on the name of the audio source at the top of the box, most people may only have one audio source, if you have multiple select through each one until sound is coming out of the correct device.
For Smart Board Speakers:
Ensure they are plugged in via USB, usually, with an USB extension cable, make sure those are connected. On the back of the speakers, there is another plugin for the USB audio cable, make sure each end of the cable is plugged in.
You will also need to ensure that the speakers are receiving AC power from the electrical outlet, they should have a green status LED on the front of one of the speakers.