I have a Mac Pro that occasionally will not boot - it basically stays grey screen instead of the apple popping up. If I shut down and start up again, it picks up just fine however. This maybe happens every 2 weeks or so. I've run disk utility to repair permissions and also from the snow leopard boot disk to fix any problems it finds already, but it's still displaying the behavior periodically. Is this a sign that my boot drive is starting to die? The Mac Pro is about 1.5 years old, but he HDD was pulled from my previous Powermac - so it's probably 4.5 years old. Thanks!