either like above, system repair.. if using an older version of windows do a google for deltree to do a reinstall. takes to long to type out, but you deltree the windows directory, rename the autoexec and config to something like autoexec.old config.old, reinstall.
If you argue with an idiot he will drag you down to his level and beat you with experience.
I am not a fast writer.
I am not a slow writer.
I am a half-fast writer.