I think your trying to change the routers log in PW?
If so, then you need to do a factory reset on the router to get defaults.
Also be aware that since this model is no longer developed on and has been phased out, some browser may not work right on it.
PC Web Browser Configurations
What browser are you using?
Try Opera or FF? If IE 8, 9, 10 or 11, set compatibility mode and test again.
Disable any security browser Add-ons like No Script and Ad-Block or configure them to allow All Pages when connected to the router.
Clear all browser caches.
Be sure to log into the Admin account on the router.
Try turning off these features in Chrome:
Top right corner, little bars for options > Settings > Settings (on left) > Show advanced settings.
Uncheck these:
Use a web service to help resolve navigation errors
Use a prediction service to help complete searches and URLs typed in the address bar
Predict network actions to improve page load performance
Enable phishing and malware protection
This router is now 6 years old. Well past a generous time frame for support and development.