javascript numbers to multiply

Hey guys I’m trying to multiply 2 numbers that are smaller than 1000 and bigger than 0 and i want alert messages to pop up if the numbers are bigger than a thousand or not a number. The problem is that the alert message shows up every time I click the button.. any tips?

function buttonAction5() {

  var z = document.getElementById("number1").value;
  var y = document.getElementById("number2").value;
  
  if (z< 1000 || y < 1000 && z > 0|| y > 0); {
    document.getElementById("result5").innerHTML = y * z;
    
  }
  if  (isNaN(y || z)){
    alert("Please write a number between 1-1000"); 
  }
  
  else (z || y > 1000 && z || y < 0);{
    alert("Please write a number between 1-1000");
   
  }

  }