asp.net - Open javascript popup on image button click -

I am trying to open a popup window when clicking the image button in the asp.net website, but when I click on the image Clicks pop up window appears for one second and then disappears. When I use the tag, it shows a pop up window, but when I try it from the other side, it disappears. Am I missing something in the code?

  & lt; Div id = "cover" & gt; & Lt; / Div & gt; & Lt; Div id = "dialog" & gt; My communication content & lt; Br> & Lt; Input type = "text" & gt; & Lt; Br> & Lt; Input type = "button" value = "submit" & gt; & Lt; Br> & Lt; A href = "#" onclick = "close pop up ('dialog');" & Gt; [Close]    
 
 
  ImageButton  - the page reappears This link shows a way to create a  ImageButton  with no popups that appear, which does not cause form submissions:  
  onClientClick = "showPopUp ( 'Dialog'); Return back;