Best answer by linuxsafer
(kav instead of KAV)
I have left it there if steady of interest.
In the meanwhile, i solutionned the problem.
It was indeed a problem of DNS server : i found the way into windows the the DNS server configuration and found that the automatical configuration had been changed to manual, adding the IP's for the DNS servers quoted in a former post.
By removing them and turning again the DNS configuration, everything was solutionned (inclusive the Windows Upgrade access).