How to recover data from locky virus affected system?

Unless you had an earlier backup, you can't. The files have already been encrypted by a strong encryption key and it would be impossible to crack it.

Thank you for your information,

there are some more techniques

1.Start system using safe mode this can work sometimes.

2.The best option is that boot system with Linux using Pendrive, you can retrieve all the data's without virus because (linux don't know what is Virus!!! :) ).

3.I think avast provides boot cleaning, repairing and detecting virus, I have done this which actually removes viruses.

In system enable system protection for all drives and Use licenced antivirus.