I recently got a mac book from my school. Last night it was freezing quite a bit so I shut it down. This morning when i boot it up I get a screen saying 'you need to restart you computer. Hold down the power button until it turns off, then press the power button again'. Each time I do this though I get the same screen. I think the start up disk for the computer is at my school. is there anyway I can get it working just for today?? I have also tried holding down F8 as i start it.