Since this issue can be caused by quite a few things this guide is going to include advice for troubleshooting both your Android smartphone and your Wi-Fi network and will begin with the more commonly successful solutions for resolving this problem and will proceed from there.

Make sure to follow all of the advice suggested in this guide. Different causes may require different methods of troubleshooting in order to get to the root of problem and prevent this from happening further.

The most likely reasons why this is happening

This is most often the result of a problem on or with the Wi-Fi network itself and NOT an issue with the
phone. If other devices are able to connect to the Wi-Fi network and seem to be working properly this can (and often is) still the result of a network related problem.

To find out for sure then you can try using your smartphone on another network. If your cell phone can connect to and access the internet with other Wi-Fi networks without any issues then you might be able to hold off on trouble shooting your phones for wifi issues for the time being and concentrate on troubleshooting the wifi network that seems to be having problems as it is likely the reason for not having an internet connection.

But we’ll get to all that a little later. Chances are good that the advice listed below will work and with any luck it should solve this internet issue with your Androids Wi-Fi connection quickly and with minimal fuss.

Soft reset the network

Performing a soft reset on your Wi-Fi network should be the first thing that you try when troubleshooting this issue, especially if this just suddenly happened for no logical reason and your phone was working fine and then just suddenly lost its internet connection.
A soft reset of your network is a common solution and can often help fix the internet on your Android phone and luckily there is no loss of data whatsoever.

Simply unplug the power cable from your router/modem wait 30 seconds to a minute and then plug the power cord back into the router/modem. It may take a few minutes for the network to start up again so give it 2-5 minutes to make sure everything was able to boot up as it’s supposed to and then check your cell phone to see if the internet is working or not.
If it is then enjoy your working internet and don’t forget to share or like this article at the bottom of this guide… if this didn’t help and your smartphone is still having trouble accessing the internet then continue with the troubleshooting suggestions listed below.

Soft reset your cell phone

If rebooting your network didn’t help then try rebooting your phone. Simply select the restart option or choose to turn it off entirely and then boot it up normally. After it reboots then test to see if the internet has started working properly or not.
If not then try performing a soft reset on the device by removing the battery while the unit is powered on, then wait for a minute, re-insert the battery, and start up the phone. Now not every Android smartphone has a removable battery so if your battery is built into your phone and it is non-removable then you can skip the physical battery pull as maybe your device allows a simulated battery pull instead. Just don’t forget to power cycle your device one way or the other. Turn it off and then turn it on.
Check your browser and home page

Make sure that you verify that your internet is in fact malfunctioning as opposed to an issue with your web browser or even worse a problematic
home page.

Open your web browser and in the address bar (where it shows what web page you are on) type in the URL of a website that you KNOW is working. I suggest typing in https://www.google.com/ or simply google.com (don’t forget to press the Enter or Search key after you have finished typing the URL in order to load the page).

If the webpage ends up loading successfully and you can perform a search through the Google search engine then that is a great sign as it indicates that there is not a problem with your phone or its internet but it’s an issue with the web page your phone is trying to load by default. Changing your phones default home page should fix this little hiccup and it will no longer appear like the internet is malfunctioning on your cell phone.
source:http://www.technetcruz.com/2016/06/fixing-your-phone-that-connects-to-wifi.html