QT4 (Linux) signal/slot question

Hello, I'm not sure this question belongs in this ng, sorry if it doesn't.

I like to learn a bit of C++ with QT4, not using the designer but writing 
all code myself. But I came to a problem I can't solve, in fact I have no 
idea whatsoever. I made a 'connect' with SIGNAL and SLOT, but it fails to 
work.

Here's a bit of code:
************************* code ************
#include <QtGui>
#include "qnews.h"

MyWidget::MyWidget(QWidget *parent)
     : QWidget(parent)
 {
        setFixedSize(600, 300);
	setWindowTitle("Vito's QNews");

	QPushButton *postButton = new QPushButton(tr("Post"), this); 
     	postButton->setGeometry(10, 260, 75, 30);
	
	//not relevant code removed here ...
	
	// here's the signal/slot command 
	connect(postButton, SIGNAL(clicked()), this, SLOT(checkFile()));

 }

// here's the function that must be executed - showing a msgBox
void MyWidget::checkFile()
{
	QMessageBox msgBox;
 	msgBox.setStandardButtons(QMessageBox::Yes | QMessageBox::No);
 	switch (msgBox.exec()) {
 	case QMessageBox::Yes:
     	// yes was clicked
     	break;
 	case QMessageBox::No:
     	// no was clicked
     	break;
 	default:
     	// should never be reached
     	break;
	}
 }
********* end code **************

But when I click the postButton, nothing happens ....
What's wrong in this code? All info very welcome.

BTW: I'm not English, sometimes understanding English docs is not easy 
for me. But I do my best :-)

Vito