On one of our macbooks the sound is grayed out and can not get it to work even after going into system preferences. the mute button is grayed and can not uncheck it

If you are using windows xp take device manager to get device manager right click the computer icon on the desk top take properties from the click hardware click device manager click the sound vedios and game controller iexpand it by clicking the " " you will find the detailes of the drivers installed if the sound driver is marked yellow uninstall it and load the drivers once again if the drivers are alreadly installed correctily check the male in conected to the speaker socket of the mother board check the volume contol wether any of the indicators is muted if the problem still presits then the problem is with the audio sockets and the audio ic if its a addon card replace it and check