Hello Dear ahsan22e
You can use this code for pop up Windows, You should change some codes:
1- Use your page name instead of Default.aspx in second Line in below code.
2- Change width or height according to your page size
3- Change menubar resizable scrolling (top left position) titlebar
Finally You should use this code on a linkbutton_Click event , I mean put a link button then double click on it and write below code on it.
I hope that it can be solved your problem.
Dim script As String = "<script language='javascript'>"
script = script + " window.open('Default.aspx', 'CustomPopUp', 'width=700, height=590, menubar=no, resizable=yes ,scrolling=yes ,top=12 ,left=12 titlebar=""HomePage" + "') </script>"
Page.RegisterStartupScript("PopupScript", script)