Could you be so kind and let us known how and what?
Audio card, audio onboard (and main board), Windows version and type (Windows 7 x64?), did it happened sudden or there was no audio ad all, did it happen after an update or a software installation/deinstallation, when using a software (like: Video/Music player) and so on.
When Windows showns an error messege, write it down and give us that information too.
How to find your Windows version and type:
Click Start, right click My Computer, click Poportions and a window will open, here you can find the Windows version you use and the type has being installed.
Ad this window you can find the hardware you have installed too. Ad the upper left corner you can click Hardware Manager and another window will be opened. See if you can find your sound hardware. If so, right click and chose Poportions, another window will open and here you can see if it's installed correct and if it's enabled or disabled.
If you like, you can update the driver from here. Just make shore that the internet connection is enabled.
If it doesn't work, you might want to deinstall it, restart your computer and Windows will install it again.
But before doing anything, let us known what you already checked.
Windows sound, is it enabled or disabled.
Go to Start/Configurations/Sound.
Check if everything has been set to enabled/not muted.
You can go to the System Tray and right click the Sound speaker, choos Mixer/Manager and check if nothing has been muted or put to minimum.
Let us know and we will try to help you!
And if you resolved it, let us know how and/or what!
Hopefully I let you known enough and that you will find the answers you seek!