I found that the quickest way to fix the problem is to unplug the router and then plug it back in. It work 75% of the time for me. If that doesn't work I use the hard reset button, hold in for 60 sec and it will restore to factory defaults. And if it's still not working then I look for the last Good firmware and install that.

BTW can you connect to the internet if you connect to the router with a cable?
Good Luck