Frustrated- There is a good chance you have a router that is failing. To be sure, disconnect the internet side, disable any security software you have (even if it seems like it wouldn't interfere), and try again. If that works, re-enable until you find the culprit. If you have access to another computer- maybe you could take the router to the computer even- it would be useful in determining quickly whether you have a problem in your PC or your router. If it is the router, the problem is likely the firmware as you seem to have suspected. There is often a means of resetting the firmware back to the factory version by performing some ackward startup routine such as holding in the reset button then plugging in the power and waiting for the LAN lights to start blinking. (I just made that up, I doubt it's correct for your router.) If it's software, well, that's a whole other can of worms. Good luck!
Others- Thanks for the ideas. The issue I was having was with accessing the config pages from my terminal server only. It would prompt me to log in, but then only show me a blank white page. After finding this thread via Google search, I decided to add the local IP address of the router to the allowed sites under the Privacy tab of IE, as well as adding it as a Trusted Site on the Security tab. It then worked perfectly. :)