You say the sound icon has gone. Have a look in Control Panel | Sounds. Under the Sounds tab, at the bottom, is Show Volume Control on the Taskbar ticked? If not, tick it.
If its greyed out, lets see if your soundcard is working correctly. Go to ControlPanel | System. Device Manager. Under Sound, look for your Sound Card. Is there a yellow ! in there?
You may also need an updated driver.
Find the name of the card, and we'll see if we can find a driver.
Not sure if this will help, but I lost my sound just last night and went through the same thing. Everything checked out, plugged in, no mute checked, etc. I had just reconnected everything after having been inside the machine and it turned out that I had put the speaker plug in the wrong port. Thought you could plug it into any that matched the little picture, but apparently not and the computer was not recognizing it correctly. When I switched to the other port, all came back up fine. So if you have recently disconnected, this might be it. I will repeat, I am not good enough at any of this to be giving advice , but since it just happened thought it might help.
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