Following on from the good advice re using SFC.
Have you by chance used a Registry Cleaner / Optimizer to clean, repair, boost, tune-up, tweak or fix your computer?
Please check Start > run > type "Services.msc" > OK > Scroll down
to "Volume Shadow Copy Service"
Check to see if it is set to either Manual or Automatic.
Restart your computer and see if you can do a System Restore.