With this Ransomware there is 2 parts to decrypting the files. The Key which is in the txt file and the 2nd part which you need to pay a ransom for. There is no other way to decrypt the files at this time without the 2 parts.
I recommend changing the drive/s and loading a clean operating system. There may be a way in the future to unencrypt the files so if you have important data keep the drive safe.
Now is a good time to look at your backups, if you don't have any it would be a great time to start.