Solution 1:
Please check your internet connectivity. Ensure that your internet speed is more than 2 MBPS. You can check your internet speed at http://www.speedtest.net/
Solution 2:
Check if you are able to open sites like google.com & youtube.com
Solution 3:
Clear your browser cache or open website in incognito (or private) mode.
Solution 4:
Some times network you are using will not be able to reach our servers. Change your system network setting to have Open DNS settings - https://use.opendns.com/
Solution 5:
Try using other available internet network like broadband internet connection.