Click on Help/update and see if you have latest.
When you say 'Stopped working overnight' I'm guessing that you mean it used to work fine but now doesn't? Are you trying to open the same RAW files as before? What camera did they come from, and as Curt asked, what version of Camera RAW dow you have (Help > About plugins > Camera RAW)
You can find a list of supported cameras and required ACR / Lightroom version here
If you think something has broken wwith your CS6 installation, lots more information please. Operating system, any other clues?
Thanks Curt and Trevor
Yes, Camera RAW has been working just fine for years. I have tried to open both new RAW files and RAW files that has succesfully been opened earlier.
The RAW files come from the same camera (Nikon D800). I can't tell you which version of Camera RAW I have since it doesn't open, but I am updating regularly using automatic notifications (Adobe Update). My Photoshop is Master Edition CS6 version 13.0.1 x64 running on a Windows 7 pc.