Currently Being ModeratedFeb 14, 2013 11:26 PM (in response to 123pest)
Mac OS X can't detect your speakers, because the volume menu in the menu bar is greyed out. First, open System Preferences > Sound > Output, and choose "Internal Speakers".
If they don't show up or, after selecting that option, sound doesn't work, reset the PRAM > http://support.apple.com/kb/HT1379 The PRAM contains your speaker information, so it will be resetted to factory settings. After resetting, sound should work without any problem and you should be able to modify the volume.
If it doesn't work, reinstall Mac OS X, and if it doesn't work, take the computer to an Apple Store or reseller to get it repaired