While there are several possible hardware and software issues that can leave a user without sound, the problem is often much simpler. Two common reasons a user is without sound are unplugged speakers and muted audio.
If you find yourself without sound, this is a simple checklist that may fix your problem sooner than sending in a ticket.
Check your speakers first. This is mostly for desktops. Though you may have not personally unplugged them, they very well may be unplugged. Your speakers wire is normally green; the speaker jack is always green. Whenever possible, plug into the rear audio jack.
If your Promethean board is without sound check the button on the side of the board. If the speakers are on the button will be green. Also, check the volume knobs on the side. If none of these are the issue try unplugging the USB connector (wireless or not) and plugging it back in; this may reestablish the sound. The below steps may also apply to your Promethean board.
Check your speaker's volume. There are often two places that control a speaker's volume: a knob on the physical speakers and a slider on the (software) desktop. You can locate the desktop slider by clicking the speaker symbol in the bottom right hand corner of your desktop. The mute button is also on the slider. NOTE: Most videos, (online or elsewhere) have their own volume slider.
Make sure the mute button isn't pressed. Some of the laptops at MCS have a mute button right on the keyboard, but on every computer (even Macs) there is a mute button on the audio slider. (see previous)
If you still have no audio after checking for these send a helpdesk ticket.