This has occured to 2 of our internal testers for the Scene Builder, using respectively Windows 7 64-bit and 32-bit.
The FileChooser does not show up (whatever the action supposed to bring it up), and no exception/ warning is displayed in the console.

Jan Stola has reproduced the problem outside of the tool, using the simple test case below (quoting him here):

"Running with assertions enabled makes no difference. I can see some debugging messages painted by the tool (like fps and memory consumption), but FileChooser still cannot be opened and no exception/warning is displayed.

On the other hand, the problem doesn't seem to be specific to your tool. I tried to write a small test-case:

package test;

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.FileChooser;
import javafx.stage.Stage;

public class Main extends Application {
   
    public static void main(String[] args) {
        Application.launch(args);
    }

    @Override
    public void start(final Stage primaryStage) {
        Button button = new Button("Show FileChooser");
        button.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent t) {
                FileChooser chooser = new FileChooser();
                System.out.println(chooser.showOpenDialog(primaryStage));
            }
        });
        Scene scene = new Scene(button, 200, 50);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
   
}

that also doesn't show FileChooser and the showOpenDialog() method returns null silently."