There is a new virus going around that is encrypting files called the "Crypto Locker Virus". There is no known fix for it just yet, just to restore from a backup. List of infected files can be found at HKEY_CURRENT_USER\Software\CryptoLocker\Files in the registry.
To Resolve: Edit
1. Read this to get further information, http://www.bleepingcomputer.com/virus-removal/cryptolocker-ransomware-information
2. Try restoring from a previous backup. This is why it it is important to backup your data.
If Windows 7, Restore From Previous Versions: