Can't connect to cable modem/router; Can't access router login

so... i've been searching around and trying ideas for three hours now. nothing. after a reset, my laptop can connect to the router AND use the internet via WiFi. i was able to use the "routerlogin.net" app once or twice to change my settings back to the way they were, yet no other device would connect and it would tell me the "modem is offline". consistantly, less said times, the router will reset, my laptop will connect with default router settings, my laptop will get internet, and i will get the message that i am not connected via WiFi when attempting to access "routerlogin.net". what the heck is going on here?