unable to access WebUI

i am not able access the WebUI on my RT-N66. i receive "ERR_EMPTY_RESPONSE" in chrome using wired connection.

i've had a tab open in chrome to monitor the 24H bandwidth for weeks (bwm-24.asp).
it was working last nite before i went to bed. this morning i wake up to find the "EMPTY_RESPONSE" error.

the browser does not popup the username/password authentication window.

i can SSH in.

here's what i've done so far: (nothing has made a difference)

restart httpd service:
$ service httpd...

unable to access WebUI