Have you installed any applications on your network that work with WiFi settings or network devices ? I installed streaming media applications on my windows pc and at least one of them altered the WiFi connection to the Router - N7 could not login as before.
I had to uninstall them and reset my Router to be able to login to WiFi again after.
Just reset my modem and switched off my nexus and it is working , I had previously in stalled an ap to use my desktop remotely and had the uninstalled it. Thanks for the help.