I have a Diemsion 8400 which recently did a strange thing - on reboot, the screen went black and a white/grey progress bar appeared close to the bottom across the width of the screen.  The bar moved very slowly and an error appeared that c:\windows\system32\config\system file was missing or corrupt.  Working with Dell techs, I could not repair , and PC Restore did not work.  I did a clean reinstall of xp home. 

 I still get this strange "progress bar" whic takes several minutes before windows opens.  (Ihave not loaded any drivers or software yet.)