Hi, I just installed Linux Mint 18 Cinnamon on my internal hard drive from USB after wiping my hard drive and I put all my files on an external usb hdd to be able to put on Linux after (was on Windows 10) now I see the external drive in Linux but when I try and open it says it is encrypted and is now asking for a password. The external hard drive is NOT encrypted.

Error unlocking /dev/sdf5: Command-line `cryptsetup luksOpen "/dev/sdf5" "luks-e8c7dbd7-80cf-433d-a4f9-0a5d323fb8a0" ' exited with non-zero exit status 1:

Before installing Linux I tested it via the USB flash drive I had, and plugged my external harddrive in to try out the file explorer and I was able to open it up normally. Now once installed I cannot open it at all. Any ideas? I am a complete noob here, am I missing something stupid? Thanks for any help.

It might be encrypted, but on the old system it was set to cache the password, or to open by a persistent key. dmcrypt would not be able to produce a luks uuid unless the drive is encrypted. There are ways to set the system to automatically open encrypted drives, the reationale being that no one can steal the drive and open it on another system.