A missing or a corrupted file, a failed update, etc., can make this application stop working. What I can recommend you is to reinstall this application, but this time you need to do it properly. First, go to Control Panel > Uninstall a program > search there SplitsTree4 > right click on it and select uninstall. After that go to its official webpage and download this application once again. After the download is complete, open the setup file and start the installation process again. I can guarantee you that this application works because I recently installed SplitsTree4 on my computer and it is working right.