I cannot hear any sounds on the computer

Make sure that the sound is not muted

Open the system menu on the right bottom corner and make sure that the sound is not muted or turned down.

Some laptops have mute switches or keys on their keyboards — try pressing that key to see if it unmutes the sound.

You should also check that you have not muted the application that you are using to play sound (for example, your music player or movie player). The application may have a mute or volume button in its main window, so check that.

Also, you can check the Applications tab in the Sound GUI:

Open Settings from the Application Menu.
Click Sound.
Go to the Applications tab and check that your application is not muted.

Check that the speakers are turned on and connected properly

If your computer has external speakers, make sure that they are turned on and that the volume is turned up. Make sure that the speaker cable is securely plugged into the “output” audio socket on your computer. This socket is usually light green in color.

Some sound cards can switch between the socket they use for output (to the speakers) and the socket for input (from a microphone, for instance). The output socket may be different when running Linux, Windows or Mac OS. Try connecting the speaker cable to a different audio socket on your computer.

A final thing to check is that the audio cable is securely plugged into the back of the speakers. Some speakers have more than one input, too.

Check that the correct sound device is selected

Some computers have multiple “sound devices” installed. Some of these are capable of outputting sound and some are not, so you should check that you have the correct sound device selected. This might involve some trial-and-error to choose the right one.

Open the Application Menu and click on Settings.
Click on Sound to open the panel.
In the Output tab, change the Profile settings for the selected device and play a sound to see if it works. You might need to go through the list and try each profile.

If that does not work, you might want to try doing the same for any other devices that are listed.

I hear crackling or buzzing when sounds are playing

If you hear crackling or buzzing when sounds are playing on your computer, you may have a problem with the audio cables or connectors, or a problem with the drivers for the sound card.

Check that the speakers are plugged in correctly.

If the speakers are not fully plugged in, or if they are plugged into the wrong socket, you might hear a buzzing sound.
Make sure the speaker/headphone cable is not damaged.

Audio cables and connectors can gradually wear with use. Try plugging the cable or headphones into another audio device (like an MP3 player or a CD player) to check if there is still a crackling sound. If there is, you may need to replace the cable or headphones.