My program is succeeding but it is showing a black screen
<pre><code>#import &lt;UIKit/UIKit.h&gt;

@interface UntitledAppDelegate : NSObject &lt;UIApplicationDelegate&gt; {
    UIWindow *window;
@property (nonatomic, retain)  UIWindow *window;
@end


#import "UntitledAppDelegate.h"

@implementation UntitledAppDelegate

@synthesize window;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.


    UIButton *playButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    playButton.frame = CGRectMake(110.0, 360.0, 100.0, 30.0);
    [playButton setTitle:@"Play" forState:UIControlStateNormal] ;
    playButton.backgroundColor = [UIColor clearColor];
    [playButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal ];
    UIImage *buttonImageNormal = [UIImage imageNamed:@"star.gif"];
    UIImage *strechableButtonImageNormal = [buttonImageNormal stretchableImageWithLeftCapWidth:12 topCapHeight:0];
    [playButton setBackgroundImage:strechableButtonImageNormal forState:UIControlStateNormal];
    UIImage *buttonImagePressed = [UIImage imageNamed:@"Crown.png"];
    UIImage *strechableButtonImagePressed = [buttonImagePressed stretchableImageWithLeftCapWidth:12 topCapHeight:0];
    [playButton setBackgroundImage:strechableButtonImagePressed forState:UIControlStateHighlighted];
    [playButton addTarget:self action:@selector(playAction:) forControlEvents:UIControlEventTouchUpInside];
    [self .window addSubview:playButton];
return YES;
</code></pre>
