Q: Problems with WiFi and Ethernet connections.

One of my 12 Macs (iMac 2GH Core 2 Duo, running OS 10.9.4) in the office suddenly is unable to connect via ethernet or wifi. The WiFi is set up on an Airport Extreme Base Station. "The cable for your ethernet is connected but your computer does not have an IP address", "Wifi does not have an IP address and cannot connect to the internet" are the messages in the Network preferences. I have restarted it several times. Have reset P Ram. Renewed DHCP lease. All with no joy. It can see the WiFi network and for ethernet the switch shows an active connection. No changes were made to any settings, it just is not connecting. Any suggestions on what to try next?