You don't mention if you application is SDI or MDI, and there are different ways of solving this....
1) SDI: Create a
Form1 myForm = null;
variable on form level in the form where you have the New menu item code. When the menu item is clicked, you do:
if (myForm == null)
{
myForm = new Form1();
myForm.Show();
}
2) SDI: You can use a boolean variable to keep track of Form1, when you open it, you set
form1IsOpen = true;
. But then you need to raise an event in the form where you have your menu from Form1 when it's closing so that you can reset the variable to false.
3) MDI: You need to loop through the open MDI child forms and check if their class is Form1.