AC1900 Model EX6400 green power light never stops blinking

do any of the other lights blinkng? 

Have you tried a factory reset? 

 

You can try recoving it with tftp or nmrpflash.  

are you on windows? if so, follow this guide

https://kb.netgear.com/000059634/How-to-upload-firmware-to-a-NETGEAR-router-using-Windows-TFTP

 

just make sure you enable tftp 

https://www.thewindowsclub.com/enable-tftp-windows-10

 

and here's a video walk through using a tftp client. Use the built in one for windows 10 though. the video is more of an example of how its done. 

https://www.youtube.com/watch?v=R9DLrLQrpaw

 

and if that doesn't work, you can try using nmrpflash

https://github.com/jclehner/nmrpflash