OnChange event problem

hi,
In my web page i place one textbox,button and required field validator for textbox.
In page load i disable my button
whenever i textchange in my textbox(onchange="function()") i called one javascript
in javascript i am enable my button

this working fine.but whenever i click button it not check asp required field validations .
i removed javascript for text box,that time validations are working fine
 
plz help me....how to solve this prob...