Q:

Pushed ViewController is "greyed out" cannot intact with it

Im relatively new to iOS programming and have been making a recipe based app for the iPad.  I've looked around at a lot of answers and can't seem to solve my problem so ill explain how my app is laid out. 
Navigation controller -> ViewController -Modal segue -> PreviewViewController -modal segue -> Navigation Controller -> RecipeViewController
Within my RecipeViewController i have a button that when pressed i want it to go back to the "home" screen which for these purposes is the "ViewController".  
Here is the code for the button action in "RecipeViewController":
- (IBAction)homeB:(id)sender {
ViewController* viewController = [[ViewController alloc]init];
[self.navigationController pushViewController:viewController animated:YES];
}

However, when i press this button the ViewController is displayed, but the screen is greyed out and i can have no interaction with the screen.  I can't post an image of what the screen looks like as i don't have enough reputation yet but i will update it when i can. 
I have tried other ways of displaying it such as connecting a segue in the storyboard between the button and the "ViewController" and then activating the segue when the button is pressed.  But this messes up other parts of my code as i have to re allocate and initialise the home screen.  Would appreciate any help as to why it is coming up with the greyed out screen that cannot be interacted with. 
Also just some more notes:
self.navigationController

does not return nil so it is seen, and no errors are displayed when the button is pressed. 
Thanks

A:

Thanks for the responses everyone, i figured out my problem though.  My structure was wrong and i realised that i didn't need to have another navigation controller for the Recipe view Controller as i wasn't pushing anywhere from there.  So incase anyone else has a similar problem my structure is now as follows:
Navigation Controller -> View Controller -Modal Segue -> PreviewViewController - ModalSegue -> RecipeViewController
I removed the Navigation controller between PreviewViewController and RecipeViewController.  This means that they are all modal view controllers.  So to get back from the RecipeViewController to the home screen which is "ViewController" i just needed to dismiss the hierarchy of modal views with the following code:
UIViewController * parent = self.presentingViewController;
[parent.presentingViewController dismissViewControllerAnimated:YES completion:nil];

I went back two stages so that both the PreviewViewController and the RecipeViewController where dismissed. 
Works great now, thanks for the help anyway everyone.