Stop the 'Ding' when pressing Enter

Try

textBox.KeyPress += new KeyPressEventHandler(keypressed);

private void keypressed(Object o, KeyPressEventArgs e)
{
    if (e.KeyCode == Keys.Enter)
    {
        e.Handled = true; //this line will do the trick
    }
}

It works for me:

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{

    //Se apertou o enter
    if (e.KeyCode == Keys.Enter)
    {
        //enter key is down

        this.doSomething();

        e.Handled = true;
        e.SuppressKeyPress = true;

     }

 }

The SuppressKeyPress is the really trick. I hope that help you.

Check out the Form.AcceptButton property. You can use it to specify a default button for a form, in this case for pressing enter.

From the docs:

This property enables you to designate a default action to occur when the user presses the ENTER key in your application. The button assigned to this property must be an IButtonControl that is on the current form or located within a container on the current form.

There is also a CancelButton property for when the user presses escape.