What model is it? Belkin or Netgear.. good luck...
Post the modems signal and log pages, did an entry there corespond to the router issue?
Do you have WAN side administration disabled?
Time server on and set to the right time zone?
it works good on ethernet but the wireless goes out have to reboot it i am on 2.4ghz on wireless time zone is right oh well if cant figure it out jsut reboot once a week been doing it awhile
get the latest firmware for the router..
Turn off WPS and any guest mode wireless.
Set it to the correct time zone and turn on the network time server.
Turn off wan and wireless administration so the settings can only be accessed by ethernet.
If it's a Netgear or Belkin, replace it