Here's the link to the apple support page detailing the solutions, but the Cliff'sNotes is the only available suggestion you haven't tried is resetting the PRAM.
The link on how to reset PRAM:
2.0GHz MacBook running 10.5. My friend's computer which he brought to me thinking I might be able to get it booted.
My buddy went to bed last night, running a video on his hard drive with the computer hooked up to his flat screen TV, he fell asleep while it was playing. This morning he woke up to a frozen screen. He did a manual shutdown. Upon restart he got a gray screen with nothing showing.
I have tried the original installation disk and restart while holding down "C" with no result.
I tried a copy of Tech Tools 5 in the DVD drive... with no result.
I have tried booting off of my own external firewire HD upon which I keep a bootable clone of os10.4.11... with no result.
I tried booting off that same external HD while holding down "C" and got the flashing folder with question mark.
I tried using a firewire cable and starting the bad macbook in target mode while hooked up to my old iBook. This caused the macbook screen to show a firewire symbol and nothing showed up on my iBook screen but an archive... Tech Tools on my iBook recognized the archive but could not Unmount the archive when I tried to use any of the tools to explore or fix the target disk.
I know that the flashing question mark indicates there is no start up software to be found, but I have to question whether this might not be something more than a bad HD. Anyone have any suggestions?
BTW... the macbook is out of warranty. My friend just went ahead and ordered a new macbook pro so there is no pressing need to get this fixed in a hurry, but he would like to get the old computer fixed if it is just a matter of replacing an HD.