After installing a new video card, (for this example an NVIDIA Quadro K620, 2 GB was used), the sound stopped working. What happened?
Some computers automatically disable the on-board video card when a PCI-E card is installed. Sometimes the sound stops too. There are a few things you can do to resolve this issue.
First, restart the system and enter the bios, (Basic Input / Output System), by clicking the appropriate key. For an HP system the key to tap is F-10, for a Dell system it is F-2. If you are not sure how to access the bios, the key to press is typically displayed during boot-up and may be referred to as Setup. Enter the bios and go to the Advanced menu. Look for the on-board sound option and change the setting to Enable, (it may be set to Auto or Disabled). Restart the system and the sound should be working.
You should also update the video cards driver by doing so through the Device Manager. This may help with future issues. Other things to try is to uninstall and then reinstall the sound card, update the sound card driver and try different sound ports to make sure it is not a hardware problem causing the issue.