My husband is trying to fix a PC and unfortunately we didn't find this site until just now. The PC was blue screening regularly and giving a c000021a fatal error message. He tried repairing the problem with the XP CD but the message 'hard error' kept coming up. He thought it was beyond repair so he decided to start from scratch with a fresh install. He reformatted the hard drive and tried to install Windows XP from scratch but a number of files could not be copied to the hard drive with 'hard error' and 'this XP CD is corrupted' despite it being a geniune CD. When the PC rebooted, it once again blue screens with the same fatal error. We have tried everything - installing onto a partition of the hard drive, resetting the bios to default, installing an older version of XP, repairing this older version with another windows XP CD. We thought the hard drive was corrupted so we bought a new hard drive but exactly the same thing happens.
I wish we'd searched your site before reformatting the drive as it looks like the problem would have been solvable but now we have a PC with no functioning operating system and a genuine XP CD that the PC thinks is a fake.
Is there anything we can do - don't hesitate to contact me if you need further information about the situation as I don't know what's relevant and what's not.