How do I regain the sound again on my PC?

How do I regain the sound again on my PC?

The normal sound level meters on Windows are all showing positive and the mute box is unticked, but when booting up Windows, there is no sound and when going into websites such as a news site where there is clips of information, the media film pictures/footage appear okay, but no sound here either.

Is there another area within Windows that controls this function?

This happened a while back but I cannot remember what started it. I currently use a LCD monitor with built in speakers. My previous plug-in speakers didn't work either. Do I need to remove a card from the PC box now that I've moved over to an LCD with speakers monitor?