Informatica 7.1 : Informatica server is not running: Problem in resolving Host while creating server in workflow

Is your sytem standalone/not connected to network?

Check in command prompt for your IP address.
For stand alone system its 127.0.0.1

Is your system connected with network/having NIC card, but you are not currently connected in network?

Connect to network.Resolve Host while creating server.Start Informatica service.