The LG W2343T does not have speakers. So you can't plug in a 3.5 mm audio patch cable between the computer's line out or headphone jack and the monitor. (Similarly, other devices can't provide sound to the monitor.)
Are you using a desktop or a laptop? If you have a laptop, make sure that the correct audio drivers are loaded for your OS and make sure that the audio isn't muted (look in the lower right on a Windows system in the tray for the speaker icon). On an HP laptop, we had to use the Component Services (Control Panel > System and Security > Administrative tools > Component Services > Services in Windows 7) and stop all audio services and restart them. Then reboot the computer to use the internal speakers at a reasonable volume.
For any unit with external speakers (required for a desktop, optional for a laptop) , connect the speakers to the audio out port (green for 3.5 mm for single connection speakers, see the manual for other speakers) or the headset port. Next make sure that the device drivers are loaded and correct for your sound card (or motherboard audio). (Control Panel > Hardware and Sound > Device Manager). If your sound isn't active, look at the Sound header. Then choose Manage Audio Devices and the Playback tab to select the desired speaker option. (Again these are for Windows 7).
If you still have no audio, make sure that the speakers have power (USB cord or AC adapter plugged in depending on the speakers). If it is USB powered, try a different port or a powered hub. If you have an AC adapter, check if it is warm. Some speakers have power/volume knobs. So check if they are on (if there is an LED, that is an easy check). If still no audio, try a different audio patch cable, if possible. Otherwise, try different speakers. There may be a damaged wire preventing the speakers from working. Depending on the problem and if your speakers are under warranty, it may be worth fixing or not.
Documentation for the monitor is available here: http://www.lg.com/us/computer-products/monitors/LG-lcd-monitor-W2343T-PF.jsp
. Click on the Support tab.
If you want to use a stereo receiver with RCA audio inputs, you'll need an adapter or a 3.5 mm to RCA m/m audio cable.
I hope this helps.