Timer for SS and global

question about global vars

I am trying to set a timer when no activity removeMovie and attach screen saver. I am trying to use a global var so that I can reset the count. Here is my AS what can I do to reset my timer.

_global.ss = 3;
countDown = function (loadScreen) {
ss --;
if (ss == 0) {
cont.attachMovie("screenSaver", "saver", 0);
timer = setInterval (countDown, 1000);

Then within screenSaver I have a function like so:

onMouseMove = function () {
_global.ss = 3;

how can i reset ss so that it will do countdown again?