No Sound

I left the nephews briefly yesterday afternoon, on the
computer and they were playing tracks on Media player.When
I booted my computer up this morning I found it was not
playing sound,with programs or when a CD is inserted.The
kids are not here now so I do not know if they have
unchecked a box with regard to sound in Media player or
elsewhere.I used scanreg/restore to return to a previous
registry but it still will not play sound.How can I get my
computer to play sound again,please? Nothing is
muted.Direct X diagnostic gives Failure at step 19(user
verification of software)HRESULT=0*00000000(error code)The
media player is showing the content bar moving and
describing the media played but no sound.Is there a tick
option pull down menu in media player or for a file that
states not play sound or always play sound that I could
check?Media player 9 installed.