When your Gmail app not working then you need to start by clearing the browser cookies and cache on the device. For this, go to computer and open Google Chrome application. Open the browser and click to more tools button and from here, clear the browser data by clicking on the option of clear browsing data. On the option of clear browsing data, click to check boxes for cookies and other cached images, data, and files for clearing. From the menu, select the data that you want to delete. Proceed to beginning of time to delete everything from browser history. Lastly, you need to hot the clear browsing data option.