tak jsem teď nakouk do práce na win7, má adresáře jinak, takže to byl postup jen pro xp.
(taky je jednodušší vzít za zdroj adresář "c:\windows\repair" se souborem "system")

win7:

Insert the Windows 7 installation CD or DVD (either full or upgrade version) into the drive and save your new settings and exit BIOS mode. When your computer starts again it will ask you to press any key to reboot from the disk. You will be taken to the Windows 7 screen. Once on this screen, you will be given the choice to install windows or to repair it. Choose repair it. If your problem is not solved try it again and this time when you choose "Repair" you should get some of the following choices: Repair Windows, Repair Using a Mirror copy previously made, Diagnose System hardware, or Display DOS command prompt or something similar.

2. Choose DOS command prompt.

3. Once on the command prompt window, type c: and hit enter.

4. Type the following commands into the DOS command prompt. Each one of these statements copy the original registry files to the current registry directory.

copy C:\windows\system32\config\regback\system c:\windows\system32\config\system