Lost IP Pass Help me

HI,

MY hax scientific atlanta 2100r2 is connected to a wifi modem( i have disabled DHCP) so its actin as a wifi router. But i have forgotten the wifi modem's ip( must be in 192.168.100 range) also forgotten its login password . Although its working good, if in future i wanted it to work as a dsl modem i wont be able to. So anyway to retrieve them?

Thanks