Could you please help us with few more details to check on this issue, what is the LED lights status on the front panel of the modem and do you have any devices connected to modem wifi network? To access modem GUI or web interface you need device connected to the modem network or to the modem directly and need to reset the modem for 15-30 secs by pressing and holding the reset button the modem to create the login credentials again on the interface.  But after resetting the modem will go to default setup any custom settings will be removed so use the default network name and password  to connect to your network.

http://arris.force.com/consumers/articles/General_FAQs/SBG8300-Web-Manager-First-Time-Login

Help I'm stuck can someone please call me

So….All I had to do was call my IP (Spectrum) and give them my MAC ADDRESS for my SBG 8300. My devices all connected automatically… but I still can’t remember the PW for my Router Gateway. I hate to reset it as I would have to reconfigure network settings on all of my devices again…

A factory reset is the only option to change the password for the GUI web portal.