Issue in opening presentModalViewController iphone xcode?

Question

i am using tabbarcontroller. In tabbar having one view.In that tab i call one function using Nstimer it open another viewcontroller.

//Third.m

- (void)viewDidLoad 
{
    [super viewDidLoad];
    [self TimerStart];  
}

-(void)TimerStart
{
    TesttabAppDelegate *delegate = (TesttabAppDelegate *) [[UIApplication sharedApplication] delegate];
    delegate.timer1 = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(targetMethod) userInfo:nil repeats:YES];
}
-(void)targetMethod
{
    [self Stoptimer];
    First * sVC = [[First alloc] initWithNibName:@"First" bundle:[NSBundle mainBundle]];
    [self presentModalViewController:sVC animated:YES];
}

-(void) Stoptimer
{
  TesttabAppDelegate *delegate = (TesttabAppDelegate *) [[UIApplication sharedApplication] delegate];
[delegate
 .timer1 invalidate];
}

Opened viewcontrller having one button.when user click that button i closed the view and call Nstimer.

//First.m

- (IBAction) Action:(id)sender
{
    [self dismissModalViewControllerAnimated:YES];
    Third *th=[[Third alloc]init];
    [th TimerStart];
    [th release];
};

The problem is first time the view opened and closed but second time view could not open.

second time i start timer in button action means it works fine...

Anyone Please help me..

Still i didn't get any solution...