sfc= System File Checker, it makes windows check all its system files to see if a newer version has been installed, or an older one is registered in the registery. Upon each file found that is conflicted, it will give you the option to use the existing or register the newer one. Always check each file shown on the screen, for version number and date, before deciding what to do. If you find a programme has installed an older version of a file, you can tell the programme (sfc) to reinstall the original, and you will need to have the OS cd-rom in the drive and point it to the windows (win98 for 98, I386 for XP), for it to do so. Don't be tempted to use the 'yes to all' function, as this may overwrite newer versions from any updates you have installed.