Your Wi-Fi network does not appear in the list of available networks, even though other networks do, or no networks appear at all. The two cases have different causes: a missing single network usually points at the router, while no networks at all usually points at the device.
The fix, in order
Check the basics. Make sure Wi-Fi is on and Airplane mode is off, and move closer to the router. On a laptop, check for a physical Wi-Fi switch or a function key that toggles wireless.
Restart the router and the device. Unplug the router for 30 seconds and plug it back in, then restart the device once the router's lights settle.
Check whether the network name is hidden. If the router is set not to broadcast its name, it will never appear in the list. Connect manually by adding the network name and password in the Wi-Fi settings.
Check other devices. If no device can see the network, the router's Wi-Fi radio may be off or faulty, so log into the router and check that wireless is enabled and the name is broadcasting.
Reinstall the Wi-Fi driver. In Device Manager, expand Network adapters, right-click the wireless adapter, choose Uninstall device, then restart so Windows reinstalls it.
Check the 2.4 GHz and 5 GHz bands separately. If only one band is missing, the router may have that band disabled, or the adapter may not support it.
Do not change router settings you do not understand, and do not reset the router to factory defaults unless you have the internet account details needed to set it up again.
If it still happens
If the network appears on other devices but never on this one, even after a driver reinstall, the adapter may have failed or may be disabled in the computer's BIOS or UEFI settings. A cheap USB Wi-Fi adapter is a quick way to confirm whether the built-in adapter is the problem.
Common questions
Why can my phone see the network but my laptop cannot? The router is fine, so the fault is on the laptop: Wi-Fi off, a disabled adapter, a bad driver, or the laptop being too far away or on a band it cannot use. Check the adapter in Device Manager first.
Can a Wi-Fi network be hidden on purpose? Yes. A router can be set not to broadcast its name, which hides it from the list. The network still works if you connect manually with the exact name and password.