Can't access C3000 Management Screen

Whenever I try to access my modem, I get a webpage saying that I am not connected to my network.Of course I am connected to the network as I am able to browse webpages, stream and anything else associated with being online.  The page recommends that I clear any cookies, history, and any data from my internet settings.  I've done this over and over and over again and still get the same error.  I have also reset my modem and started all over again.  After resetting the modem, I get a good 5 minutes or so and then I start receiving the same error.  What else can I do?  Thank for any assistance.  Oh, this started happening today (07/12/2020)  As far as I know, there was not update to firmware or any push from my my ISP.