A corrupt monitor profile, mnost likely.
Reprofile the monitor, or set it to sRGB; then restart Lr and see how things look.
Hello dear members,
indeed the monitor profile was'nt good, I have changed the profile to sRGB IEC61966 – 2.1. and now i can see the images perfect.
Many thanks for yours reactions ! Tanks Keith Reader en F.Mclion especially !
You 've made my day very good ! Tanks a lot !