[RT-AC68U] Router won't boot up (only USB 2.0 LED lights up)

I bought the RT-AC68U last December and have been very happy with its performance up until about two weeks ago. The wifi (I only use 5Ghz) stopped working on my devices even though all the lights in use on the router were still on - including the 5Ghz light. I restarted the router and it worked fine for 10-20 minutes and then the same thing happened - all lights indicated normal operation but wifi was down. This time I tried plugging in an ethernet cable and I got a link on my computer...

[RT-AC68U] Router won't boot up (only USB 2.0 LED lights up)