The first thing you should do for fixing your sound is check your speakers volume level, and make sure you did not mute Sound in your computer’s operating system by checking your system trays volume icon’s volume level. Also, make sure your speaker wires, and power are properly plugged in.
You can check if your speakers are working by unplugging them from your desktop computer, and using an MP3 player or CD player to playback music via the headphone jack connected to your speakers’ plug. You can also take out your desktop computers sound card, and test it on another computer to see if it works on another computer, or you can move the sound card to a different PCI expansion port if you have a empty PCI port on your computer’s mainboard.
For laptops, you can boot your computer into a liveCD operating system like Ubuntu to check your speakers sound is working in Ubuntu if it is it means your speakers are fine, but your installed operating system is not detecting your sound card or your speakers are broken/disconnected.
If you notice the sound is crackly, squeeky, or distorted, it could mean your speaker wires are broken, your speakers are failing, or you turned your volume for your speakers too high on your speakers.
You should go online to download the latest or previous version of your sound card driver from your Desktop computer maker, or your sound card maker if you notice your computer previously had sound, but lost sound because you installed the wrong version of a driver.
In Add/Remove programs which you can find in the Windows Control Panel, you can uninstall your sound card driver by looking for it.
You can also type in Device manager if you used Windows 7 or Vista to launch it. There would be a section called Sound, Video, and Game Controller where you can right click it to uninstall the driver. You can also right click your sound card in device manager, and pick properties. In the drivers tab, there is an option called Driver roll back.
If your sound problem was recent, you can just do a system restore to an earlier time when your sound is working properly.
Also type Sound in your Windows 7, or Vista start menu. This will launch the sound wizard. Right click the white space and make sure show disabled devices, and show disconnected devices are checked in the right click context menu.
If a device like your speakers or mic is disabled, you can right click the device and pick enabled. If a device is disconnected it means your speakers or mic is not properly plugged in, or it is broken. Check to make sure the speakers and mic are plugged into the right port on your sound card, and your speakers are powered on. Also, if you installed your sound card make sure it is seated correctly in the PCI expansion slot. If it is a USB sound card, try another USB port.
For Linux computers, in my experience, either sound cards work or they don’t. You can try searching your sound card company website for a Linux driver, or just install a new sound card. Also, make sure your speakers are not muted by checking the system tray where you can usually adjust the sound levels for your operating system and programs.
In my experience, C-Media, and Realtek  branded sound cards work pretty well with Linux operating systems.
If you notice some sound files which can’t be played back like ogg , you may need a codec. The Kazaa lite codec pack and other codec packs can help with this problem. Some players like VLC player, SMplayer, and Mplayer can also play sound and video formats which other players can’t play. Linux distros like Ubuntu can automatically detect which codec you need to install in many cases when you are using Totem media player to playback sound.
Good luck fixing your sound!