qDebug() is a output stream special for debugging. It doesn't represent the debugging process in its whole.

About QVector,I can see a lot of improvement here:

First, You're not modifying your QVector, so you can put it const. This is useful to avoid bugs (Nice!)

Second, because you're not inserting in the middle of the "Container" then you don't need QList (QList is much more inefficient that QVector)

Third, QVector<QString> can be easily replaced by a QStringList. Look in documentation for its advantages.

Then returning to the code:

index in this way:

while{
    if{
       }//end if
    else{

     }//end else
}//end while

Regardless what @Eeli-K said about qSort(), I think you need to practice more programming in general. Qt is facinating, all I know I learned programming in C++/Qt. Check some books, DEBUG, and enjoy.

... If you finish debugging and you have a good question, please look at us.

Thanks

Your code structure is something like

if 
    for
        if
            while
                if
                else break
                if
                   for
                   for 
                       qSort(VectorAux.begin(), VectorAux.end());  
                       if 
                           if 
                           else if
                                 else

First, it's difficult to read, understand or debug with any method and it's very error prone. After you have solved one problem you may run into another. You should rewrite it to be clear, easy and self-documenting. Second, you use qSort in n-th level inner loop which is probably inefficient (how many times it's executed?). Third, there might be (not necessarily) good candidates for C++ standard library algorithms like find_if which should be preferred to custom loops, both for error-freeness and readability.

Ps: The problem happens in the moment when a function is called.

Are you going to modify the DiasOrdenados, if not? Better use QVector.

Then, your indexes are kind of confusing, please comment the end of the parenthesis.

I Recommend you to debug, do you know how to debug?

Thanks

for(int i = 0; i < DiasOrdenados.size(); i++

Not only that part you said but all the content it continue failing. The difference happends when that for is present, that is the inflection point

Easy, You are modifying the Vector Aux size indirectly with the functions:

Prepend()

And RemoveAT()

Please modify your implementation.

 for(int i = 0; i < DiasOrdenados.size(); i++)

it continues crashing close to 6500. If I comment that loop it does not crash (i mean // for(int i = 0; i < DiasOrdenados.size(); i++)). I dont understand why that for is causing a crash.

HEADER ventanas1.h

n = 0;
QList<QString> DiasOrdenados << LUNES << MARTES << MIERCOLES << JUEVES << VIERNES;

SOURCE ventanas1.cpp

void Ventanas1::on_pushButton_clicked(){
    n++;
    qDebug()<<"n es"<<n;
    val = 1;
    cont = 0;
    z = true;
    if(n <= 10000){/ 
        criterios();
    }else{
        ui->pushButton->setStyleSheet   ("background-color: QLinearGradient(spread:pad x1: 0, y1: 0, x2: 0, y2: 1, stop: 0.0" + Vint[2][0] + ",  stop: 0.4" + Vint[2][1] + ", stop: 1.0"+ Vint[2][2]+");"
                                        "color: #868479; "
                                        "border-style: solid;"
                                        "border-style: solid;"
                                        "border-radius: 7;"
                                        "padding: 3px;"
                                        "padding-left: 5px;"
                                        "padding-right: 5px;"
                                        "border-color: #339;"
                                        "border-width: 1px;"
                                        "font:Bold;"
                                        "font-family:Georgia"); //Problema potencial 1. Solo una vez permite meterle el stylesheet.
        ui->pushButton->setText("No hay más\nopciones");
        ui->pushButton->setEnabled(false);
    }
}


void Ventanas1::criterios(){  
    if(Mnh < 8){ 
        qDebug()<<"entro";
       umero = 0;
        for(int i = 0; i < DiasOrdenados.size(); i++){ //In this for happends my problem
                if(DefDias.count(DiasOrdenados.at(i)) > 0){ 
                cont = 0;
                val = 1;
                while(cont < DefDias.size()){
                    if(DefDias.indexOf(DiasOrdenados.at(i),cont) != -1){ 
                        IndCriterios << DefDias.indexOf(DiasOrdenados.at(i), cont);  
                        cont = DefDias.indexOf(DiasOrdenados.at(i), cont)+1; 
                    }else{ 
                        break;
                    }
                }
                if(IndCriterios.size() > 1){
                   for(int j = 0; j < IndCriterios.size(); j++){ 
                       VectorAux << DefHoraF[IndCriterios[j]];
                   }
                   for(int h = 0; h < VectorAux.size(); h++){
                         VectorAux.prepend(DefHoraI[IndCriterios[h]]); 
                         qSort(VectorAux.begin(), VectorAux.end());  
                          if(VectorAux.at(0) != DefHoraI.at(IndCriterios[h])){ 
                              if(VectorAux.at(VectorAux.indexOf(DefHoraI[IndCriterios[h]])-1) - DefHoraI.at(IndCriterios[h]) + Mth < 0){ 
                                  val *= 0;
                                  numero++;
                              }else if(VectorAux.at(VectorAux.indexOf(DefHoraI[IndCriterios[h]])-1) - DefHoraI.at(DefHoraI[IndCriterios[h]]) + Mth == Mth){ 
                                  val *= 1;
                              }else{
                                  numero++;
                                  val *= 1;
                              }
                          }
                          VectorAux.removeAt(VectorAux.indexOf(DefHoraI.at(IndCriterios[h]))); 
                   }
                }
                IndCriterios.clear();
                VectorAux.clear();
            }

        }
    }

    on_pushButton_clicked();
}

PS: I dont know if recycling variables is causing that problem. Because I used some variables like cont and var several times in others methods.

Please, give us more context if you want help... Specific questions.

you do not mechanic " hey, my car stops 2 minutes after I start engine, could you fix it without seen the car?"
I like when people trust in me as I were a god, but I can't give you an useful answer.

If you are unable to do it yourself you display the part of the code around the crash (typically a function) and people might try to help you.
What you stated provided no information which could help people even to guess. And no - there is no limits on the loops.

Find what makes it crash and then fix that.