Hmm, just now when i pointing my mouse over my dock there, the dock dint enlarge and those expose functions are all off. Then i decided to restart my it, but it stuck at the shutting down screen for quite a time. So i press my power button to force it off, but then when i trying to switch it on again, my mac stuck at the white apple screen for few mins. the loading circle is not moving at all. And i do force it off and switch it on. luckily this time my mac back to normal. just want to ask that is this thing caused by 72hours running of machine?