Same thing here. I upgraded the firmware, because our company got a call from our ISP that we might have malware on our router. Apparently the stock firmware is vulnerable to attacks.
Since we have quite a few settings on the router for our printers and security system I took a backup so I could restore the setting after upgrading. After the reflash and settings restore, everything is working ok, but I can't access the router. Afterwards our ISP said they highly recommended doing a full reset and not restoring the previous backup, because of the malware. This wouldn't be a problem if I could just check what the settings are and then do a full reset. I haven't set up the printer and security myself so I have no idea what those settings are.

Help needed.