So I have been using LR 5 no problem for 6 months and have imported Sony, Fuji and Canon RAW files no problem.
Today it won't recognise RAW files any more. Viewing the new images in Library module I see "Preview unavailable for this file"
Then when I try to import "This file is not recognised by raw format support in Lightroom"
I have the latest version (5.7.1) and it's CR2 (Canon RAW) I'm trying to import from a 760D which is apparently supported
I'm on a PC, Windows 8
The 760D was first supported in LR 6/CC 2015.0, not in LR 5.7.1. LR 6.1.1 is the current version but a paid upgrade from LR 5.x.
Cannon 760D support was added in Lightroom 6.0 and I believe that is the reason of not being able to import the images in Lightroom 5.7.1
You can refer this article which states that you need Lightroom version 6.0 and Camera Raw 9.0 for these raw files : Cameras supported by Camera Raw
Or, you can use the free DNG converter to convert the images into DNG and then, import them in Lightroom 5.