Long shot - press the Windows key and R together then type on
services.msc
and hit Enter. Is the Service named "Volume Shadow Copy" Manual or Automatic? If it's automatic, you may have a system backup of all your files which are probably unaffected because the extortionists aren't smart enough to trawl the system for copies. If Manual, sorry - no joy but I have to disagree slightly with mrmez - there's no guarantee and, in fact, little chance of actually getting a decryption key from them even if you pay.
Long shot #2 - did you check to see if they deleted all your System Restore points? If not, try going back a day or two.
If you do contact them, make sure you also use The Onion Router because once they have your IP...