A computer has no sound if its speaker volume set to the mute level. Check the volume by double-clicking the sound icon in the Windows notification area.
Sound card driver errors, including driver conflict or missing sound card driver, also cause a computer to lose its sound. Open the Device Manager in Windows, and check if there is a yellow "!" or red "X" beside any device. Check the Sound, Video and Game Controllers category in the Device Manager to make sure that the computer has a sound card driver installed. Additionally, a computer with no sound card or a failed sound cars has no sound. Verify the status of an on-board sound card in the CMOS setup.