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http://tinyurl.com/g4bv8
This will work in the majority of cases unless you have corrupted the Registry and then you'll need to perform a new install of Windows.
As you can read your data without any problems you don't need to worry about Taking Ownership of the files or any form of encryption being used so I would suggest that you backup everything of any importance then wipe the HDD and perform a clean install of Windows on it. You can download Boot & Nuke from here
http://tinyurl.com/4rfur
This will write zero's to every sector of the drive so there is no possibility of anything that was wrong with the previous installation being carried through to the new installation as to the installer the HDD will look like a new clean unused HDD that you can install Windows upon.
Once you have Windows Installed load an AV Program and update it and any other M$ products that you intend to use once you have this done and it's working correctly you can activate the copy of Windows then log onto their Update Web Site and install any available Updates Service Packs and that will be all that is required.
When this is finished you can copy your data back to the HDD and replace all your data back to your My Documents Folder as well as your Favourites and the contents of your E-Mail Client and Address Book by importing these last two directly into your Mail Client.
Col