Go to Control Panel \ Sound and Audio devices \ Volume tab \ select the "Silence" box and uncheck it immediately. If the audio doesn't come back right away, check the box again, Apply and Accept, and again open Sound and audio and this time remove the check mark from silence, Apply and Accept.
If audio doesn't come back after this; Open Sound & Audio devices once more, click on the Audio tab, and copy the Default Audio Device name (from the dropdown window) to paper,.. and next go to the Start button \ click on Run \ and type "compmgmt.msc" (no quotes) and hit Enter. Next click on Device Manager, and browse down to Sound Video and Game devices, click on the boxed plus sign and select the device that matches the name you copied from the Control Panel, right click it, and select "Uninstall" and restart the computer.
If audio is still not available, go again to the Sound and Audio device name in the Device Manager, and select Update Driver \ select "Not at this moment", next, select "Automatically install the software (recommended)" and click Next. The driver should automatically reinstall and if it doesn't you willl have to download it fresh from the Audio device maker's website or from the motherboard maker's downloads section.
Install Speccy to know the audio device or motherboard name and model to search in the maker's website for the sound card driver.