I went through most of these suggestions last night to no avail. Lastly I tried to upgrade via the firmware restoration program. I did it exactly as described. Turned off the router. Held the reset button and turned it back on and waited for the power light to flash (flashes very slowly). I then used the utility and it would upload the firmware and go through the entire 'system recovery' process and would get to 100%. After it finishes it says it failed to connect to the router and to check that it is in recover mode. I tried at least a dozen times (varying lengths of holding the reset button). When I did the upload and it was going through the recovery the power light stops flashing. Not sure if that is supposed to happen or not. If it isn't, what should I try differently?
Unfortunately now I can't even get to the GUI of the router and all routing functions have stopped working (still lights up and powers on except for the wireless lights). I am writing this at work. Hopefully this isn't a hardware issue.
'Are you upgrading through the Check button, or through a file located on your local PC? The second method is the most reliable one.'
I tried both methods. I always go through using the file on my local machine but when that was not working I tried the check button which didn't work either.
'Make sure you upgrade it using a wired, and not a wireless connection'
My desktop is connected to the router with a wired connection.
'Also make sure you have the right firmware (RT-N66U or RT-AC66U).'
Double checked. All of them were for the correct router.
'Finally, try a different web browser in case it's an extension or an add-on in your browser blocking it.'
I haven't tried that yet, I've upgraded the firmware several times with my browser with no issue. I will give that a try tonight if I can (since the GUI is not working right now). I currently use IE9.
Apologies for the loads of info, figured it was better then not enough.