[Costin Trifan]

Firstly, welcome to v7n, mrjokers!

Now, to answer your question:
1. you need to delete one line from your code (the bolded comented one):

    var el = document.getElementById(element);
        el.style.left = cur.offsetLeft+"px";
        el.style.top = cur.offsetTop+cur.offsetHeight+"px";
        //el.style.display = "block";

2. add this lines of code:

	if ( el.style.display == 'none' ) {
		el.style.display = 'block';
	}
	else {
		el.style.display = 'none';
	}

3. finally, your code should look like this:

function show(cur,element) {
    var el = document.getElementById(element);
        el.style.left = cur.offsetLeft+"px";
        el.style.top = cur.offsetTop+cur.offsetHeight+"px";
        
    document.onclick = function(e)
    {
        var obj = document.all ? event.srcElement : e.target;
        
        if (obj != el && obj != cur) {
        el.style.display = "none";
        }
    }
     
     if ( el.style.display == 'none' ) {
	el.style.display = 'block';
     }
      else {
             el.style.display = 'none';
       }
}