Sounds like its giving your PC an external IP... mine has the same problem with this version.
Go into your nic settings, and set up a static IP, something in the 192.168.1.xx range, With 192.168.1.254 for the gateway. Then you should be able to access it. (Or use another computer)
Yes, you are right. My comp is receiving external IP. Even when I set IP 192.168.1.5 to my comp I could not access the modem as 192.168.1.254. It looks like the modem is in the bridge mode How to switch it back? Reset button does not help