Cannot edit or overwrite in explorer hosts file, even as admin
The hosts file may be protected by Antivirus or other security software, check for that and temporarily disable it prior to making your changes.
Alternately, this has worked for me in similar circumstances: Open the Windows Explorer with 'Run as Administrator' (ctrl right-click ...) then in the ..\etc\ folder create a file 'new_hosts' as you wish it to be, rename 'hosts' to 'old_hosts' then rename new_hosts to hosts, restart the network service or reboot.