1. Always use official launcher to start your game, don't use game exe without it, and make sure you are logged in to the launcher using your forum credentials.
2. Make sure that no antivirus software is blocking launcher and game.
3. Check your firewall it may be blocking connections for launcher and game.
4. If above steps doesn't work, try to re-install everything.
I hope those 4 steps will be enough to help with your issue.