It happens some times when some of the windows system files got corrupted with time due to various reasons.
If you want to delete a system file in Windows XP you may be able to do it easily just by renaming the system file and just refresh the folder view. After refresh windows XP will create the missing file automatically or otherwise you will need to close and reopen the explorer window for that folder.
But In Windows Vista you can delete or replace a system files, even with administrative privileges. The default windows service called TrustedInstaller protects all the system files by default which will keep protecting the system files and prevent it from getting overwritten.
Today we will tell you how to replace or delete system files in windows both manually and by using software.