When you manually change the permissions, make sure that it is the Administrator account that is enabled. Change the permissions (after making sure that you are the owner under Details) to Read and Write (I'm sure that this is what you tried).

If nothing works, do the more expensive and time-consuming thing: a back up of alll files and a clean Install of OSX by completely erasing the HD (and any partitions).

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-