The Windows Security Center service is turned off

My wife is having her weekly PC issue...

The Windows 7 Action Center is displaying the following message:

Windows Security Center Service (Important)
The Windows Security Center service is turned off.

When I press the "Turn on now" button, I get the following error:

The Windows Security Center service can't be started.

I ran Avast Free and found no viruses. I ran Autoruns and found nothing unusual either.

Any ideas?

I'm not quite sure what I did, but I restored to a prior checkpoint and used my repair disk to fix startup problems. The system is operating normally at this time.