open a new window.

to open a window:

1) In page_load:

Button1.Attributes.Add("OnClick","javascript:window.open('popupnew.aspx','','width=300,height=200')");

Or

2)In btn_click

string popupScript = "<script language='javascript'>" +
"window.open('PopUp.aspx', 'CustomPopUp', " +
"'width=200, height=200, menubar=yes, resizable=no')" +
"</script>";

Page.RegisterStartupScript("PopupScript", popupScript);

Can't we open a new window with out using Java script.

The simple answer is NO

The reason is clear, however. Just because you view the page you created with ASP.Net in a browser doesn't mean it's a client scripting language

ASP.Net is a SERVER-side platform- Javascript is a client-side scripting language