Unable to connect to internet

I am new in linux. I am using ubuntu 8.04. I worked in internet from ubuntu. But when My internet provider changed  ip address , I can`t access web. I edited network setup. But I could not found any benefite. I used XP and ubuntu duel. But with this same network configuration i can access internet from XP. I can`t Understand what is the problem??my network configuration is perfect. When i command ping <my default gateway> , result: "Network unreachable".  I repeat "" My ip, gateway, dns are ok.provider only change only ip address : to;   and eveything are remain same.What should i do??I hope, somebody will help me.