The problem should be fixed now. A DNS change has caused this problem. Now, the base DNS configuration has been restored. Please clear your cache and cookies and check if this issue is fixed, as it should be.
If it's not, here are some different operations that can help to fix the issue :
Close your browser
Reboot your Internet connection
Clear the DNS cache with an ipconfig/flushdns process (How to do this ?)
If that still doesn't work, save your current DNS info somewhere else and try to change temporarily your DNS for the DNS provided by Google (How to do this ?)
Thank you very much to all of you for your patience