HTK

I have Windows 10, made a backup on Sept 2016, on an external harddrive. Recently got trapped with the Ransomware Locky virus, some files encrypted and no success in saving them. I tried to run my backup drive and file, but for some unexplained reason, my current Win 10 will not/does not recognize it. Any suggestions? I got to one page/info box that said the external drive was not NTFS format, and yet, I have not changed the format on the desktop since upgrading to win 10. and making the backup.