my.enable_click = on;

later then
if(event_type == event_click) 

function Main
{
level_load("prjectd.wmb");
wait(2);// at least, you need to wait until
        // the level is loaded completely.
}

function Main()
{
   level_load("prjectd.wmb");
   wait(1);

   mouse_mode = 1;       // enable engine mouse
   mouse_range = 20000;  // Range within click, touch, or release events of 
                         // entities can be triggered by the mouse (default 
                         // 1000 quants. Copied from the Menu ;)

   
   while(1)
   {
	mouse_pos.x = mouse_cursor.x;   // keep the mouse pointer synchronize
	mouse_pos.y = mouse_cursor.y;   // with the engine mouse.
	
	wait(1);
   }
}