Gridview Page Refresh

Question

Hi All,

             I need help, I have one grid view and inside the grid view I have image button which I create using Item template in grid view.

I am opening new popup window on image button click in grid view. It works fine I am able to open popup window on image button click.

the prob is when after clicking on image button selecting grid whole page is refreshing after opening the popup and the previous textbox data will loss i am not able to insert.

I want to stop that page refresh. Please help me..