Please refer Thumbnails display black in Lightroom CC 2015.2/6.2 to resolve issue with Black thumbnails while importing.
As your images are turning Gray.This happens when you have a corrupt monitor profile
- Exit Photoshop Lightroom.
- Open Color Management from start menu search.
- Click the Advanced tab.
- Change the Device Profile to a standard RGB color profile sRGB IEC61966 - 2.1
I have tried what you said but It doesn't work either, I have noticed that the images are not gray what happens is that a gray square appears instead of the images.
I also have tried deleting the previews and generating it again, and now I can see the images only in the develop module.
Thank you for your support
Did you restarted your Computer after selecting the sRGB IEC61966 - 2.1 profile from Color management Window?
I made a custom profile and it works, but I guess it would have worked also restarting my PC, anyway thanks for the help
Glad to know it is working!
The grey thumbnails are a symptom of a display profile that is incompatible with LR. Windows 10 installs manufacturer-supplied display profiles, displacing whatever profiles were previously assigned to the display, and LR doesn't like these profiles. Changing the display profile to sRGB or recalibrating your display (if you have a calibrator) fixes the problem.