WNDR3400 Blinking Power (Green)

First try to do a hard reset, press the pinhole for 30 seconds. If that doesn't help it out I think you'll have to try debricking the router. I think the firmware upgrade got corrupt when updating for some reason. If you know how to ping your router with the command prompt just wirte ipconfig and see if it gives a response. Also, to debrick the router you'll need to download a program called tftp2.exe and use that along with the firmware bin that you tried earlier and load it with tftp to the router. Watch a few videos on youtube called "how to debrick a router" and follow those steps and it might make it work again. I've done this before so sometimes it works.