Why is my computer not recognizing my speakers or headphones?

Check sound settings in Control Panel to make sure speakers or headphones are set to default.
If using external sound device, make sure it is connected to the right port.
Check audio jacks to make sure they are secure and not loose.
Restart the computer to re-connect the default configurations of soundcard or audio driver.
Right-click audio icon on taskbar at bottom right of screen. Select Playback Deviced, then Properties. Make sure correct device is active and selected as default.
Check audio cable connections to ensure they are firmly connected.
If you are using a HDMI connection to external speakers, ensure the connection is secure and not loose.
Re-install or update audio driver and sound card under Device Manager.