My mid 09 macbook pro has been shutting off during reboot , at exactly 12 seconds every time! What does it mean?
It sounds as if your system isn't finding a boot drive. Which version of OS X are you running?
A faulty power supply will cause this. Try and run the Apple Hardware Test, if you can. Otherwise, make an appointment at an Apple store or AASP:
I am running Mac OS version 10.4.6
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