Hmmm...I think I am getting some hints.
BTW which browser are you suing? Is that Internet explorer? If yes, my first advice will be switch over to firefox or opera because they can handle javascript without causing severe frustrations to the user.
But if you are already using firefox, then probably there is some javascript issue. What may be happening is that CPU usage shoots to 100% and your PC freezes.
Next time, just open the task manager(Ctrl+Shift+Esc) and check the CPU usage while this happens. Also are you using the firebug extension with firefox? It is known to shoot ur CPU usage to 100% on complex/long javascripts.