for this use session ,, store counter value in session and every time when page_load then increase the counter by 1. and same save in the session.
and check session value in condition :
count=0;
protected void Page_Load(object sender, EventArgs e)
{
count++;
Session["count"]=count;
if(Convert.ToInt32(Session["count"])==1)
{
button1.Enabled=true;
button2.Enabled=false;
button3.Enabled=false;
button4.Enabled=false;
}
else if(Convert.ToInt32(Session["count"])==2)
{
button1.Enabled=false;
button2.Enabled=true;
button3.Enabled=false;
button4.Enabled=false;
}
.
.
}
Hope this will help you.
Don't forget to mark as answer if it helps. :)