Look to see if a second cable connecting the audio input monitor output of the computer sound card. If it is, and the sound is still there, first, try to find on the front panel of the monitor button with the symbol of a crossed speaker. Click on it and then either over it will turn off the led, or the screen will go into stand dynamics, but not crossed. This means that the sound is enabled. Pressing the button again will cause the receiver diode or the emergence of symbols crossed out the dynamics - the sound is muted. On some monitors a separate button to change the mode of the speaker no - this feature can be enabled and disabled via the menu.
If the monitor is brought out of shutdown mode sound, but to hear anything fails, look for the volume control. Even on the monitors, where all adjustments are performed electronically, such a controller can be analog. Turn the handle, and the sound should appear. If the handle is missing, look on the front panel arrow buttons, which is located between the symbol dynamics or try to find an item to adjust the volume in the menu on the monitor.
It is impossible to rule out incorrect configuration of the mixer of the operating system - but then the sound will not be in the case if you connect to the sound card with regular speakers. Run the appropriate tool (its name depends on what you're running) and check if you have turned the audio output.
Even if the cable exists, not the fact that it's connected properly. Check whether it is connected one plug to the green socket of the sound card and into the monitor socket marked as Audio in. If necessary, install the RAM in the correct slots. In addition, the cord may be faulty. To find out whether this is so, disconnect it from the computer and from the monitor, and will ring the ohmmeter.
In the absence of cable look for it in the packing box of the monitor. If he is not there, and there manufacture it themselves. Take the two 3.5 mm stereo mini-plug standard Jack (TRS). Three-wire cord, connect the corresponding contacts.