Write the code for validations in the button control.

In 4 Text boxes properties, make the cause validation 
property false. And in button click event make the all text 
box cause validation property true.

If we want the validation to be done after the click event 
of the button 
we can set the disply property of the validator to dynamic 
vaidaton will occur so when user click on button 
and not on when user left the field invalid 

but as answr above 
cause validation property is used to avoid the validation 
to occur on some respective buttons

if we want to validate only few controls on page 
then we use the valiationgroupproperty  to set it with same 
name to all controls in group and of the validator