can't add table rows

hello
 
i have two buttons in my page and there is one html table and anothe is ASP table. what i want is, when  i click on button1 a row add in the table with 3 columns but when i again click on that button it dosen't add new row and the same happen with asp table.
second problme is, if i click on button1 it add one row in html table and than i click on button2  to add row in asp table it remove the row which i add by clicking button 1. same thing happened if i click button 2 to add row and than click button 1 it remove row added by button 2 event.

 protected void Button1_Click(object sender, EventArgs e)
        {
            
            HtmlTableRow addrow = new HtmlTableRow();
            Table1.Rows.Add(add ...