This problem can occur due to different reasons and some of them can be related with your computer/browser.
We suggest you start by checking the speed of your internet connection here and follow these steps:
• Refresh the page (press Ctrl+F5)
• Close all web browsers and re-open the website
• Clear your cache memory (Ctrl+ Shift+Delete, and select everything except the passwords for verification) Still not working?
• Check your Flash, Shockwave and Java versions—these plugins might need updating.