unable to access the sp 2010 url after change in IP address of servers

hi,

 We have developed and deployed a KM portal using sp 2010  at customer place. it was running  successfully till last week,

 what teh customer did, last week, they changed the IP address of the servers where sharepoint, index srvr etc were hosted.

 Now when they  try to access the KM portal, they were unable to access the appln.

1. IP address of SP server :-xx.xxx.x.xxx"
2. ip of iondex  :- xx.xxx.x.xxx
3. ip of DB server  : -xx.xxx.x.x
4. BackUp  server ip address :xx.xxx.x.xx

what may be the reason for this .

pls help.

what steps need to be done   in order to get the  appln  running.