|Look for a wee icon bottom right of the screen (there will be quite a lof mini icons there); see if one is loudspeaker... If it's there, right click on it and see if you have simply "muted" the audio/sound output. If so uncheck the tick box...|
This "walk though" may also be of help; as it takes you (step by step) though the whole windows-7 audio/sound controls system:
You click on the "arrow head" to the right of the initial image to step through it all.