Odd audio question

Hi! New here! One day my computer stopped showing the ''sound'' icon in the lower right box by the clock. I could click on it and adjust my volume. Now its gone and when I click on Start>Programs>Accessories its gone. the only thing there to click on now is 'sound recorder' and when I click on that it tells me I don't have an audio device installed yet I have sound I just can't adjust it!! any ideas?
 
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