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Via the keyboard
Many laptops have a shortcut on the keyboard which allows you to enable and disable the Wi-Fi adapter, as quickly as possible, and some laptops have an indicator (small light) which blinks when the adapter is on. This is the main Wi-Fi on/off switch, i.e. you won't be able to activate the module no matter how hard you try, if it was disabled via the keyboard shortcut.
If the Wi-Fi indicator doesn't blink, it is possible that you have accidentally disabled the wireless adapter while working on your laptop. To enable the Wi-Fi adapter or disable it, press and hold the Fn button and the Wi-Fi dedicated button (the button with a wireless-antenna icon).