I'm having issues registering the Cisco IP Phone 8851, Product ID: CP-8851-K9= that is at my workstation. The power cord is connected and an Ethernet cable is plugged in, but the phone never registers. The display has indicated that it's registering for the past 48 hours. There's no dial tone. The only thing that seems to be functional is the display screen. I'd appreciate any troubleshooting advice from the forum. Thanks. Bryan