Something is wrong with my code

I am making a music maker program in C# (visual studio).
Here is my code:

int accCount = 0;
enum accidental { flat, sharp, none }
accidental thisAcc = accidental.none;
if (keyComboBox.SelectedItem.ToString().Length < 8)
{
   MessageBox.Show("Please select a key!");
}
else switch (keyComboBox.SelectedItem.ToString())
{
    case "C major - A minor":
        accCount = 0; thisAcc = accidental.none;
        break;
    case "G major - E minor":
        accCount = 1; thisAcc = accidental.sharp;
        break;
    ...etc..
}

and so on...
This all is included in postButton_click(postButton_Click(object sender, EventArgs e)
But when I click the button, an exception is shown
(An unhandled exception of type 'System.StackOverflowException' occurred in Program.exe)

And if I select "break", this line is selected:

object key(int count, accidental ac) (here is the cursor){ 
    return key(0, accidental.none); 
}

Does anyone know what is wrong?
Sorry if this question is not specific enough, just tell me.