SB6190 Unable to login to modem

I have a Surfboard SB6190 cable modem and I cannot login to it. I type 192.168.100.1 into the address bar an hit enter. That brings up the Arris login page with boxes for username and password. I try my last known good username and password and get an error message: "invalid username or your access has been locked due to multiple failed login attempts". So I attempt to reset the modem to factory defaults by depressing and holding the button on the back of the modem for ten to fifteen seconds, unitl the lights on the front shut off, then I allow it to turn back on. At this point the username and password should be reset to the factory defaults of admnin and password, but still no dice. I've tried this several times and I always get the same error message. Does Comcast lock users out of their own modems? Did my modem just take a dump because they are cheaply made?