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/
Clear your browser cache or open website in incognito (or private) mode.
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/
Try using other available internet network like broadband internet connection.