Try adding the IP for the modem or router into your browser network connections "no proxy list" .... This has been known to fix issues with connecting to the modem / router in the past. Very easy to do.
For Firefox: Tools, Options, Advanced, Connections, Settings ... no proxy list is in there, but you will need to click
on Manual Proxy radio button, then enter the IP's you want to bypass the proxy / internet .. Then recheck "No Proxy" button.
Internet explorer is similar to do.