A few days ago my internet connection stopped working using wifi on my Desktop, tablet and phone. 

I can still connect and it is showig full signal on the router and the devices but the internet connection does not work. I have been using it problem free for months. 

I have tried restarting the router and disconnecting from the network on my devices and reconnecting but none of it has remedied the problem. 

What could be the problem?

Thanks, Christoph