From a Google search I think you are talking about an E- Machines computer, model T3312 (You didn't actually say what machine it is, so I'm guessing. You may get better results if you give all the relevant info in your question.)
If I'm right, that I have to ask: You installed the operating system, but did you install the drivers? Specifically the sound card driver?
EMachines support is here: http://www.emachines.co.uk/em/customercare.do?ctx1w.att21k=2&LanguageISOCtxParam=en&sp=page11l&CountryISOCtxParam=UK&ctx1l.c2att1=17&rcond3l.attN2B2F2EEF=3624&rcond4l.attN2B2F2EEF=3912&CRC=99015199
Come on, you did look on the maker's site?
You can also check out this discussion thread: http://www.dexplor.com/phpBB2/viewtopic.php?f=12&t=7750071
Google is your friend.
D'Underhead
May 2010
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.