Since upgrading to this new release on my RT-N66U I have been having trouble with the DHCP settings page. The webUI navigates to the page, but it is missing the navigation side bar and top menu bar and the apply button does not work or make any changes. Any suggestions?
Upgrading from what ? If it was an old firmware you may need a factory reset.
Have you tried a different browser?
Have you rebooted the router?
Try powering off the router at the socket, leave for 5 minutes then power on again.