AC66U - won't start after flashing, recovery mode doesn't help

Hi
I have big problem after trying to update firmware from 376.49 to 378.51_beta1.
At first everything looked as usual - I've choose new .trx file and upload it with web GUI. Waited some time for the progress bar to fill up and then I tried to hard reboot. But router didn't respond after. All I can see is CFE miniWeb Server and power LED slowly flashing.
I tried to do factory reset (reset button + power on) and it did put router into recovery mode (flashing LED). It even response to ping. But now two solutions that I found doesn't work and I have no idea what to do next:
1. Using CFE miniWeb Server - tied to upload new and old version always have same results - first I'm getting immediately browser alert that connection was reset and nothing happens. If I try to upload again router stops responding and...nothing happens.
2. Asus Firmware Restoration - can't find router in Recovery Mode...even if I see it laying right here, flashing its LED at me. What is interesting - after trying to upload this way router stops response to pinging. It looks like it freezes or something.

I found some threads about "bricking" router but those problems seemed to have at least option to upload firmware using tools above.
Any suggestions?

Make sure you downloaded the correct model. Disable all security software on your PC, and try a different browser.

I think you were impatient and corrupted the firmware you were trying to install.

Why would you hard reboot? Did the messages indicate the update was finished?

Version is correct.
I tried IE instead of FF. They're was no "connection resets" message but after a short while browser was redirected to /f2.htm with message that this page can't displayed. LED is sill flashing slowly...but I can't get to upload form again. Should I wait? Is there chance that there is something happening right now and that is why I can browse this form even if router still responses to ping?

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There was a message that firmware was successfully uploaded and now I need to reboot it manually in order to proceed (or something like that)...this wasn't the first time I was updating my router .

With the RT-AC66U I recommend waiting a good 10-15 minutes when flashing through the recovery process before manually rebooting the router. Usually a manual reboot isn't necessary - you should see the router has rebooted when the wifi LEDs are back online (assuming you didn't had wifi disabled).

Ok...that's weird. Leaving it for couple of hours did help somehow and recovery software manage to detect it and restore firmware to its former glory.

Now if only I could find out why WAN won't work. Each cable is connected as usual, configuration is on auto and yet there is no connection to isp. There is nothing in logs about it so I even don't know where the problem can be...

edit: Ok...never mind - problem solved itself during night - when I woke up everything was running as usual.