By restarting your device, you will kill all the processes running in the background as well as the one which might have prevented you from connecting to Wi-Fi network(s). Also, you will reset the Wi-Fi card (or adapter), which might have failed to load properly.
"Forget" the Wi−Fi network and reconnect again to it
Consider "forgetting" the Wi-Fi network, especially if you reset your router and entered the same wireless network name (and password), but, before that, you were able to connect to that Wi-Fi network.
To "forget" the network, follow the below-mentioned steps:
Go to Settings, select Wi-Fi and enable it by moving the slider to the right.
Tap on the Wi-Fi network you want to "forget" and select Forget This Network.
You won't be able to connect to Wi-Fi, if you don't enter the correct password. Make sure that the password is entered in a correct way, as passwords are case-sensitive (e.g water is not the same as WateR).
"Forget" the Wi−Fi network and reconnect to it again
Consider this as an option, especially if you reset your router and entered the same wireless network name (and password), but, before that, you were able to connect to that Wi-Fi network. You need to remove the Wi-Fi network from your mobile device's saved Wi-Fi passwords list, i.e. "forget" the network, and reconnect to it.
To "forget" the network, follow the steps below:
Go to Settings and tap on Wi-Fi;
Tap on the Wi-Fi network you want to forget and tap on Forget.
After you have "forgotten" the network, reconnect to it.
Your device's inability to connect to Wi-Fi networks might be due to a hardware-related issue, usually with the device's Wi-Fi module. In this case, consider taking your device to a repair shop, only if you have tried all the other solutions, including resetting your device to its factory settings, but none of them worked.
Move the device as close to the router as possible
Maybe your device doesn't connect to the Wi-Fi network, because it's not within the router's range. Try moving the device to the router as closely as possible and you should be able to connect to the network.
Make sure that you are trying to connect to the right network
Maybe the real reason for this issue is that you are trying to connect to another Wi-Fi network which has a similar SSID (name) as your own. Double-check the SSID of your Wi-Fi network and compare it with the one you see on your device and make sure that they are identical.
Some Smart TVs have an inbuilt Wi-Fi module, whereas others need a Wi-Fi dongle which is sold separately. If your TV needs a USB Wi-Fi module to connect to the Internet, make sure to insert it in the TV.
You can enable the Wi-Fi module in Settings -> Network (depending on the brand).
Maybe the network you are trying to connect to is hidden. If this is the case, you need to connect to it manually.
Click the Wi-Fi icon in the upper right-hand corner of the screen and select Join Other Network...
Enter the network name, select the security type, enter the password and click on Join.
Watch this video tutorial on how to connect to hidden Wi-Fi networks:
Note: The most common security type of today is WPA 2 - Personal (also known as WPA 2 - PSK). You can also check the check box next to Remember this network, so that you can easily reconnect to this Wi-Fi network in future.
Maybe the problem is not in your device, but in the router, i.e. the way it's configured. In this case, try resetting the router and then reconfigure it again, i.e. start from scratch. On most routers, there is a small reset button on the back side. Once you press it (on some routers you need to use a toothpick to press it), you need to access the router (see the don't know how to access my router guide) and select a network name and a password.
If you tried all the other options to resolve the issue, including reinstalling the computer's operating system, or taking your laptop to a repair shop, but nothing worked, you should replace the Wi-Fi adapter. Alternatively, you can buy an external, USB wireless adapter, which is sold separately.
Consider this as an option, only if you tried all the common solutions to connect to Wi-Fi network(s), but none of them worked. Please bear in mind that by resetting your device, you will delete all the data (photos, videos, music, etc.) stored in its internal memory, therefore, make sure to make a copy of them.
Maybe the Wi-Fi network you are trying to connect to is hidden. In order to connect to hidden networks, you need to enter the router's details (SSID and wi-fi password) manually.
There are two ways of connecting to hidden Wi-Fi networks:
Via the Notification area
Click on the network-bar icon (in the bottom right-hand corner of the screen) and click on Hidden Network.
Type the network name and click Next.
Type the password and click Next.
Follow any additional instructions, should there be any.
Via the Network and Sharing Center
Go to the start menu and type Network and Sharing Center;
Click on Set up a new connection or network;
Select Manually connect to a wireless network and click on Next.
Enter the Wi-Fi network's (router's) information, i.e. the SSID, password, etc. for your network in the appropriate fields.
Note: In the Security typefield you need to choose the type of security used by the hidden wireless network, which can be found on the router's label on the bottom side, closely to the model number. Also, Windows may or may not ask you to also specify an encryption type, depending on the security type you choose. Please bear in mind that WPA 2 - Personal (or WPA 2 - PSK) is frequently and widely used these days.
Note: If you want to connect to this network automatically, check the check box next to Start thisconnection automatically. Also, you can check the check box next to Connect even if the network is not broadcasting.
Consider this as an option, especially if you reset your router and entered the same wireless network name (and password), but, before that, you were able to connect to that Wi-Fi network. You need to remove it from your computer's saved Wi-Fi passwords list, i.e. "forget" the network, and reconnect to it.
To delete saved networks, follow the steps below:
Click on the start menu and select Settings (the gear icon);
Click on Wi-Fi and select Manage known networks;
Click on the Wi-Fi network you can't connect to and select Forget;
Select the network, click on Connect, enter the username and password and click on Next.
Note: If you use Windows 7, right click the Wi-Fi network icon in the bottom right-hand corner and click on Network and Sharing Center. Then, click on Manage wireless networks (on the left side of the window), select the network you want to "forget" and click the (-) remove button.
Consider this as an option, especially if you reset your router and entered the same wireless network name (and password), but, before that, you were able to connect to that Wi-Fi network. You need to remove the Wi-Fi network from your computer's saved Wi-Fi passwords list, i.e. "forget" the network, and reconnect to it.
To "forget" the network, follow the steps below:
Open Network Preferences at the bottom of the drop down menu;
Click on Wi-Fi (located on the left side) and click Advanced (located at the bottom right of the pop-up window);
Select the Wi-Fi network you want to "forget", click the minus sign and click OK;
Reconnect to the Wi-Fi network by entering the username and password.
Updating the operating system is a must, in order to improve the mobile device's functionality and eliminate bugs in the operating systems. Usually, the updates are being applied automatically, but sometimes this is not the case.