Try exiting it out and try again. It did that briefly on one of the workstations here in the office, and restarting it seemed to help.
You can also try adding the game folder/files to your exceptions list in your antivirus and firewall software. Please see the help menu or support website for the software that you use if you aren't sure how to do it.
At your own risk, you may have to disable your antivirus, firewall, and other security software temporarily while you download, install, update, login to, and play the game. Sometimes the security software will block it or throttle it, no matter what you try or even if you try to add exceptions for the game files in your security software.