In the majority of cases, following one of the suggestions below will solve the problem:
- Refresh your browser page.
- Quit and restart your browser.
- Quit and restart your computer or device.
- Try a different browser such as Firefox http://www.mozilla.org/en-US/firefox/new/ or Chrome https://www.google.com/intl/en/chrome/browser/
Clear your cache. Visit: http://www.refreshyourcache.com/en/home/ and follow the button for the browser you are using.