Windows form stop button Actions

Question

I have a windows form which has :
1. Browse button(button1,button2,button3)
2.Check button 
3.Start button
Once Start button is pressed I don't want other buttons(1 and 2 ) to work  (if user click on it once start is pressed he should get a message that program is already running )at the same time I don't want the  buttons to grey out (button.Enabled =false will grey out the button) I want to disable button action and not the button