I'm having a problem with my MacBook- for the past month or so the only way I can shut it down is by pressing down the power button. When I hit shut down or log off on the apple menu nothing happens at all. The same applies for e.g. when the software updates require restart- when the computer prompt comes up to restart and i say ok, nothing happens. I bought my computer in March 07 and it's OS X 10.4 tiger (I think!) Can someone tell me what I need to do -is it just a pathway that's missing and how do I fix it?