[AC Question]

The message I have is that the wifi signal is good, but whenever I try any kind of connection e.g. the web or Gmail I receive a message to try reconnecting. In 'Settings' I get the words: 'Authentication problem'.

[Rukbat]

You're connecting to a wifi signal that requires a password - it's either the wrong password (or you spelled it wrong, or you're using the wrong case) or there's something wrong with the router you're connecting to.

All routers come with a default name - like Linksys routers all show an internet connection named linksys. You could be trying to connect to a neighbor's signal that has the same name as yours - but the password is different.

Try connecting to a public wifi hotspot, or to a friend's wifi (with permission, of course - and you may need the password). If that works, the fault is almost definitely not with the phone. If it doesn't, your phone's firmware may be corrupted. (A reflash would fix that.)