As long as you have external speakers plugged in, the screen's speakers are disabled.
Click on Windows10 search icon (bottom left corner, near the start menu, if not using the metro interface) and enter something like "audio manager" or "realtek". You will find this way your audio card control panel. Or, as others suggested, open old and good Control Panel (not windows settings) and look for something related to audio.
Also, usually (if not previously disabled), when plugging in headphones or speakers on the audio-in socket, a pop-up window should appear asking you to choose the type of the device just plugged-in.
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