Here is the manual for your modem.
http://www.timewarnercable.com/Media.../RCAdcm425.pdf
Are you connected through the USB port? If yes, plug ethernet ASAP!!! USB cable with connections is totally crap and to be avoided at all costs with P2P.
Can you connect with 56K modem (phone) to see if you are still firewalled? (ie we'll know if the prob is the modem)
Ciao