A quick Google search shows that .ctbl files are a sign of a cryptolocker virus, a particularly nasty virus that encrypts all your files and holds them for a ransom, usually the virus will notify you that you need to send a certain amount of money to them for them to unencrypt the files. Unfortunately, if they really did encrypt your files, you probably will not be able to unencrypt them. You would need their encryption key. It's possible that it's a fake cryptolocker virus and that it didn't actually encrypt the files. Try copying one of the files and renaming it back to "filename.txt" and see if it opens.
Either way, you definitely need to post in the Am I infected? What do I do? forum to see if you are infected and find out how to remediate.
Do you have any physical backups of your files?