Untitled

form should not appear after the 30 button_click
private int counter = 0;

...
counter++;
var form2 = new Form2();
form2.ShowDialog();
...

...
if (counter < 30) {
    counter++;
    var form2 = new Form2();
    form2.ShowDialog();
} else {
    MessageBox.Show("Sorry, Form2 has already been opened 30 times.");
}
...

static int count;

if(++count <= 30)
{
    //show it
}
else
{
    //Do something else
}