SanDisk flash drive---Can files be un-encrypted?

If there was a way to get them un-encrypted the security wouldn’t be very good.  Have you tried using the SanDisk help site?

https://kb.sandisk.com/app/answers/list/kw/will%20my%20cruzer%20work%20on%20windows%208%3F/sno/1/search/1/session/L2F2LzEvdGltZS8xMzY2ODI5MzEzL3NpZC9xem4xR3hvbA%3D%3D

The reason why you got prompted for a new password is a bit of a mystery.  Did someone try to access your files?