Once every ninety days, I always find someone who needs help fixing audio volume issues. Because of the frequency of this issue, I can usually find the issue within five minutes and resolve it within ten minutes.
Look to see if the mute notification is located on the lower-right of the Windows Taskbar. If the mute notification is missing, check to see if the volume is too low to be heard then increase it to 50% or more. The default volume level is 67% or 2/3. On macOS, the mute notification is on to the upper-right of the Menu. If the notification is missing, launch the System Preferences app from the Dock then access the Sound submenu.
Check around the computer for external speakers. These are often at the side but may be mounted to the bottom of the monitor. If the computer is equipped with external speakers, make sure that it is powered up via USB or an adapter (a red, green, or blue light on the speakers should indicate this) and that all the audio cables are undamaged and plugged in correctly into each other and the sound card in the rear of the computer. To lock or unlock Dell speakers from a monitor, see the instructions.
Check the volume percentage for each program (YouTube, Windows Media Player, VLC, etc) that creates audio as the setting can be off or very low which is why the main volume has no effect.
Check to see if the (audio) drivers on a Windows machine are installed and also installed correctly. If the device never had sound, then you may have the wrong drivers. If it had sound before, the drivers are possibly corrupted and should be removed and reinstalled. Before attempting to do this, try and save your files and then restart the computer as 60% of the time, a hiccup makes it appear the drivers are corrupted so restarting can save you valuable time. On macOS, drivers or kernel extensions should not be an issue unless it is a Hackintosh so you will have to see if the kext version is correct for the bootloader and OS version along with FakeSMC or VirtualSMC.
Save any necessary data then unplug, if any, external speakers while the audio should be playing. This will let you know if the speakers are damaged as the internal speakers should start working. If there are no external speakers, power off the desktop or tower computer so that you can check to see if there is an internal speaker located inside the computer and if the speaker is securely attached to the motherboard or if the leads/cable is damaged. Note that some computers (server grade) do not have internal speakers and will have to use external speakers or headphones. Others, have their internal speakers on the outside and are called AIO or All In One and are similar to an iMac in looks and can have a mute button on the bezel.
Audio can be disabled in the BIOS as well for internal speakers and is usually done by an IT Department for public settings such as classrooms and libraries to limit disturbance to other users or to prevent you from listening to movies and music all day instead of the task at hand. Be aware the BIOS may ask for a password to make any changes. Although the internal speakers are disabled, the headphones should still work and Bluetooth if it slipped their minds.
If you want to test if your internal speakers are undamaged, try removing the RAM (while the unit is off and unplugged) and then try to boot the unit. The unit should beep to let you know the RAM is missing also confirm the speakers are plugged in properly and is undamaged.