If you are experiencing issues starting Zoiper on MS Windows you should always first check the configuration of your security software.
For example, if you run Zoiper5, but you are stuck on a white screen, or nothing happens, you may need to add Zoiper as exception for your security software. This may be your Antivirus, firewall or something else that you are using.
Currently known to cause issues during launch(Zoiper does not launch or stays "white"), for example are:
If you cannot see video during calls, so as your camera's preview, the issue is most-likely caused by your firewall. Zoiper streams the video on the localhost, thus using third-party firewall may block the connection.
Currently known to do so are:
Note, other security applications could also cause similar issues, thus if you experience one of the problems above, refer to your security software's manual or support department.