Aporte original por: fairleymac ,
First, I would try booting from your OS CD. If booting from the CD is intermittent, or doesn't work, you know you still have a HW issue. If the CD works without issue, simply reinstall OS X. You have a F***ED hard drive. Also, have you tried (or did the technician) a different set of RAM in the machine? Although it does sound a lot like a logic board issue, bad RAM might display the kinds of issues you're describing.