powerbook startup problem - folder with a question mark ???

[Sebastien G <sebas-listes@koumbit.org>]

Hi all,

  I have a powerbook g4 550 running all the time Debian unstable with
kernel 2.6.8-powerpc and OSX sometimes, mainly for spike.

  For the last week or so, when I start the machine instead of having
the yaboot screen appears I get a little folder with a question mark
inside...  This doesn't happen every time I start the machine.

  When it happened the first time, I booted with a debian bootable
install cd and the hard drive was not recognized.  (???)  I booted with
the Apple Hardware Test, run all the tests and it didn't find any
problems.  I waited a couples of hours and then the machine booted
fine. ?????

  I have been trying to identify a pattern but no chance.  I use my
laptop everyday and the problem never occurred in the morning at
startup.  So far, I had the problem almost systematically after I leave
work and then go to some place and boot the machine.  Note that I always
do a clean shutdown.  I then wait a couple of hours and then it boot
fine.

  What could it be, firmware? hard drive?  Is there any software to test
the machine?

  Any advices, ideas, would be great.

Thank you.

Sébastien