The thing is there are a lot of potential reasons why this could happen. Some systems have complex audio setups, USB devices, HDMI devices all of which can cause Windows to change the default audio playback device for any given system.
What we can do is point you in the direction of where the default playback sound settings are to be found, but without anything regarding even the spec/model of laptop, what display devices its connected to, or USB audio devices it may be connected to there is little else anyone can do to help.
Because you haven't specified the Operating System I'm going to assume you are using Windows 10, however your ability to access some settings may be restricted due to the version of Windows 10 you are running.
1. Move the mouse pointer to the start menu button.
2. Right click on it and select "Settings" from the menu.
3. In the Search Box type in "Control Panel"
4. Click on the provided Search result icon.
Once the Control Panel is open you can pin it to your taskbar for ease of access at a later time.
5. Within the Control Panel Left click on the icon labelled "Sound"
6. This should open up a window labelled "Sound" That has three tabs. We're only interested in the first tab "Playback"
7. In here you should see a list of detected Sound devices installed in your computer. Being a laptop The most likely playback device to be used is going to be "Speakers"
8. Left click on this device, then left click on the button labelled "Set Default".
9. If this still does not work but there are other devices listed, you can also try those in turn to see which is capable of producing sound.
There you have it, if there are further issues, please get back to us, and also if you can please provide some detail on your laptop because that will help immensely!