Why do you create a timer2 object inside data::event() function (is it a slot?) ?

When you call data::event() again, there will be another "timer2" object and can cause memory leak (if your application doesn't freeze).

I suggest that you declare timer2 as a member of your class, create timer2 object in your constructor, set the interval, then connecting timer2 timeout() signal to your warning_timer2() slot.

Qt Code: 
  1. data::data(...)  : ...
  2. {
  3.    ....
  4.    timer2 = new QTimer(this);
  5.    timer2->setInterval(300000);
  6.    timer2->setSingleShot(true);
  7.    connect(timer2, SIGNAL(timeout()), this, SLOT(warning_timer2()));
  8.    ....
  9. }
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Then, in your data::event()

Qt Code: 
  1. void data::event ()
  2. {
  3. // Qtimer  *timer2 = new QTimer(this);
  4. // QObject::connect( timer2, SIGNAL(timeout()),this,SLOT(warning1_timer2()));
  5.  
  6.    if (((condition1)||(condition2))&&(warning1) ) //Conditions
  7.         {
  8.              warning1=false;
  9.               int  answer = QMessageBox::warning(this, "Problem detected",QMessageBox::Ok);
  10.                   if (answer == QMessageBox::Ok)
  11.                      {
  12.                       // timer2->start(300000);
  13.                         timer2->start();
  14.                      }
  15.         }
  16. }
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