cannot access the router after firmware update

[Carnegie]

I have had Nighthawk AC 3600 Tri-Band Wi-Fi Router R7960P working fine. Since the firmware update was available I updated it and now it says it is R8000 and it is not accepting my user name and password. I tried everything I knew. Please help.

[plemans]

anytime you have issues after a firmware upgrade, a good place to start is factory reset the router and manually re-install. 

have you tried this? 

[michaelkenward]

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@Carnegie wrote:

Since the firmware update was available I updated it ...

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How did you go about the process? Manually? With the browser graphical user interface.