If you're using Google Chrome, please go to this link: https://support.google.com/chrome/answer/95472?hl=en.
If you're using Firefox, please go to this link: https://support.mozilla.org/en-US/kb/pop-blocker-settings-exceptions-troubleshooting.
If you're using Internet Explorer, go to this link: http://support.microsoft.com/kb/843016.
Please note -- We highly recommend using Google Chrome as opposed to other browser types. This can be downloaded easily by Googling "Chrome download".