What is the default password for airstation Nfinity WHR-HP-G300n

i found this might help http://setuprouter.com/router/buffalo/whr-g300n/manual-1481.pdf

The WHR-G54S has a default LAN IP address of 192.168.11.1
and Subnet Mask of 255.255.255.0.
Make sure your computer has an IP address in this range 192.168.11. x
Open your browser
type http://192.168.11.1
you will enter the web interface of the router
root is the username and no password is needed.
Configure your router.
http://cdn.cloudfiles.mosso.com/c85091/WHR-G54S-Manual-v1.9-web.pdf

Did you loose WiFi access password or router password?
If it's WiFi password then you can connect over Ethernet cable, login to the router (default password is blank) and change WiFi password.
If it's router password you will need to reset it to factory defaults and setup everything from scratch.

Here is the manual with the details.
Wireless Configuration, p. 40
Factory Reset, p. 67
http://cdn.cloudfiles.mosso.com/c85091/WZR-G300N-Manual-v1.1-web.pdf

Most Router have a Reset button on the back of them you can hold in for about 10 seconds and it does a factory reset on that router. I would suggest to try to do that first.
Below is the manual to your wireless router>
http://www.lmi.net/wp-content/uploads/WHR-HP-G300N.pdf

1. Update your iPhones software.
2. Reset the router and follow the setup instructions from scratch.
OR
1) In your browser type in AP's IP address (default is -> 192.168.11.100)
2) type in root as user name and keep password field blank. hit enter.
3) To connect wireless devices to the AirStation, you may either enter the SSID and encryption key manually, or you can use AOSS.( these settings can be found under wirless config tab)
for detailed information about configuring ap refer this manual
-: http://cdn.cloudfiles.mosso.com/c85091/WHR-G300N_Manual_web.pdf

Most passwords are
admin or
password

Default login:
root is username:
password remains blank.

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309

Download Latest Driver And Utility,Install WHR-G300N in Next USB Port and also check any other Software related WiFi.
Uninstall in safe mode del temp file then install.

If you are using the router as an Access Point, 192.168.11.1 wont work unless it is in Router Mode. You should find out LAN IP for the G300N, and use that to access it with username "root"and nothing for the password.

192.168.11.1 is for:
Moderm >>> WHR G300N >>> Computer

LAN IP is required to access
Moderm >>> Router >>> WHR G300N (Access Point Mode) >>> Computer

Work and play - further and faster! Your AirStation Nfiniti combines Ethernet networking with extended wireless range and speed. It offers excellent compatibility with most wireless clients, giving superb performance with Wireless-N, Wireless G, and legacy Wireless-B clients. For best overall performance, use with Buffalo Technology Nfinity wireless clients. System Requirements: • A high-speed (Broadband) Internet connection or existing local area connection. • A computer with a network connection (wired or wireless) and a good web browser. The screenshots in this manual were taken with Firefox, but Netscape and Internet Explorer are also supported in versions 4.5 or later, and Safari 1.0 and later are supported with Macintosh OS X 10.2 and later. Package Contents: • WZR2-G300N AirStation with built-in antennas • AC adapter • CAT5 LAN cable • Utility CD with Manual • Quick Setup Guides • Warranty Statement

see link for details and a fix for your issue http://cdn.cloudfiles.mosso.com/c85091/WZR2-G300N_Manual_web_new.pdf