var x = 5;
var y = 1;
var z = 0;

function startClock(){
  x = x - y;
  setTimeout("startClock()", 1000);
  if(x==0){
     z = z + 1; if(z > 2) z = 0;
     x = 3; switch_promos(z);
  }
}

function switch_promos(id){
  for(i=0;i<=2;i++){
    if(i==id){
      document.all("style_"+i).style.display = "block";
      document.all("mobile_"+i).style.display = "block";
      document.all("print_"+i).style.display = "block";    
    }else{
      document.all("style_"+i).style.display = "none";
      document.all("mobile_"+i).style.display = "none";
      document.all("print_"+i).style.display = "none"; 
    }
  }
}