First, we start with checking your phone. If you cannot use the WhatsApp account on your smartphone, you cannot use WhatsApp Web either.
Part 1: Check Phone Connection
Part 2: Check Computer Connection
Part 1: Check Phone ConnectionStep 1. Send Messages
Try sending some messages to your friend and see if it successes.
It is obviously that my "Hi" was not sent.
Step 2. Follow the Connection Troubleshooting Steps
When this happens, you can click the following link to find solutions for you phone.
Android | BlackBerry | Nokia S40 | Nokia S60 | Windows Phone | BlackBerry 10.
Here I would like to make a brief introduction about the Android solutions.
1) Turn Wi-Fi off and on.(Setting > Wireless & networks > Wi-Fi)
2) Connect to a different hotspot.
3) Reboot your phone.
4) Enable data. (Settings > Wireless & networks > More… > Mobile networks)
5) Make sure that your APN settings are correct by calling your mobile provider.
6) Check for the latest version of your phone operating system.
7) Turn Airplane mode on and off.
8) Upgrade your WhatsApp. Download a new one at the WhatsApp website.
9) Reboot your Wi-Fi Router in case there is something wrong with it.
11) Uncheck "Restrict background data" by going to Settings > Data usage > Menu Button > Restrict background data.
12) Make sure that your APN setting is correct by calling your mobile provider.
When all these are done, I believe your phone can send a message again. Now try using WhatsApp Web. If it still won’t work, there must be something wrong with your computer connection.
Part 2: Check Computer ConnectionStep 1.Log out and in
If you are sure that the internet connection is normal, trying refreshing the page by hitting "F5" on your keyboard. When the problem still exists, press the menu button . Choose "Log out". And follow the instructions on the website to log back in.
Step 2.Update the Browser
Please note that only the latest version of Chrome, Firefox, Opera and Safari is supported. (Not Internet Explorer) Check for an upgrade.
Step 3.Unblock the Website
It could happen that your network administrators in your companies or collages limit connections to WhatsApp. When this happens, you can get a notification that your Wi-Fi network is preventing WhatsApp Web to work correctly. Contact they to get the website web.whatsapp.com and *.whatsapp.net unblocked.
Hope it helps! Any questions about how to connect to WhatsApp Web is welcome and feel free to leave a comment.