title: Place form on top and disable others behind it
body: <p>I have a Main Form and a Other Form.
  The Main Form is always open, and at some time it will launch Other Form.</p>
  
  <p>I tried:</p>
  
  <pre><code>form.TopMost = true;
  </code></pre>
  
  <p>But this only places the form on top. The Form behind (Main Form) still can be accessible.</p>
  
  <p>How can I get the same behavior like when I do OpenFileDialog, and disable the main form behind it?</p>
  
  <p>(Thanks in advance)</p>