all your data has gone away.
The fact that you booted the machine up would indicate that, at the very least, there is a fully operational OS installed on the drive.
Clock resetting is sometimes an indication of a dead or defective battery.
You will have to be a little more specific about what has actually happened and what you can currently see on the desktop of the booted machie.
Can you see the HD, usually in the top right of the screen? What happens when you double click the HD icon.
Do you see a Users folder? What is inside it?
Define "all updates removed". What version of OS X is now on the machine? Exactly what were these updates?
P
i have an iBook G4, 768 MB ram, 60 GB HD, 12". I have tiger installed as an upgrade, and there were few, if any problems. Recently, after changing no system files or deleting anything, the computer truned on and there were no files. All my data had been erased, the clock reset, and all updates removed. It had been more than a month since upgrading to tiger, and like i said, the computer had turned off just fine, and then when i booted it up, everythhing was gone. I am currently on a PC because i find even them more reliable then if this was going to ever happen again.

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