Nighthawk RAX40 Connect Internet Issue (Tablet, Mobile and Desktop Computer)

Hi Team, 

Last night 11PM the internet suddenly got disconnected across all my devices (Tablet, Mobile and Desktop Computer). I confirmed with my broadband company that there was no internet outbreak across the city and they could detect optic fibre internet connection to my nighthawk router, so I could confirm that it's solely my nighthawk's issue not the modem from the internet company. 

The "internet" icon was off and resetting/rebooting takes much longer than usual. Even this morning I could only see the lights on for power, 2.4 GHz and 5 GHz. I have done:

- Unplugging and repluggin all wires, both internet modem and nighthawk
- Resetted my nighthawk by using a needle to hit the button
- Turning it on and off, both internet modem and nighthawk
- Unplugging and repluggin all adaptors, both internet modem and nighthawk
- Tried to use my phone to connect to the router via the nighthawk app - didnt work

This evening when I got home I saw the internet light is finally on so I tried to connect again. It said DNS server was not responsive so I followed youtube video to manually override the DNS server - Works great and I'm typing out this question now via my computer

Andriod phone didnt connect so I manually override the IP address (Used a different one than my computer) and works now - great

Ipad didn't work even if I manually override the DNS server and/or change the IP address. 

Tried to log into the nighthawk app and I think it was able to detect my nighthawk. But username is defaulted and locked at "admin", which made me think it restored back to some factory setting. I remember the back of the router said default password is "password" so i entered that and said wrong password. I also tried my original nighthawk account password and wifi password but didnt work.

I have 3 questions if I may:

- Why did this problem randomly occur?
- What else should I try to fix my ipad connecting to wifi?
- How can I reconnect & relogin back to nighthawk app? 

Thanks very much team for looking into this