Question: I have a form that takes user input and then let the user get connected to the sql server.
This is happening on button click.But where can I set the property Default button so that the user when clicks enter do the work of that button.

Answer: 
It is called `AcceptButton` now on the form; set that to the button that will be the default button.  

Refer to [Form.AcceptButton Property](http://msdn.microsoft.com/en-us/library/system.windows.forms.form.acceptbutton%28v=VS.100%29.aspx)
I think you want the "AcceptButton" property at the FORM level... That will expose a combobox of available controls on your form, then select your "button" you want to use as the "Default" button on enter.