How to Enable/Disable Href link at code behind

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C#

ASP.NET

Hi...
I want to Enable/Disable Href link according some conditions but how i don't know...???

Only Enable/Disable not Visible/Hide...

I have used following code but it's not working..

<a href="User.aspx" id="href_user" runat="server">User</a>

code behind

if(session["Admin"]==null)
{
href_user.Disabled=false;
}
else
{
href_user.Disabled=true;
}