hiding a control in C# and ASP.Net is easy.
simply add the attribute runat="server" and id="id" to the control for example,
<div runat="server" id="samplediv" style="height : 100px; width : 100px; background :red;"></div>
now in code behind it is simple to hide the control on either page load or button click or on whatever the event you like to use hide the control.
hide control on button click
protected void btnHide_OnClick(Object sender, EventArgs e)
{
samplediv.visible = false;
}
hide control on page load
void Page_Load(Object sender, EventArgs e)
{
samplediv.visible = true;
}