Error 678 Connecting Through WAN Miniport PPPoE

Causes
The cause of Error 678 on a WAN miniport using PPPoE can be difficult to track down because it can occur in a variety of circumstances. On Windows XP computers, this error may appear after upgrading to SP2 and then attempting to connect to the Internet. Disconnected network cables, a disabled modem, corrupt drivers and damaged Winsock settings will cause this error. In addition, third-party firewall programs may block the WAN miniport. Spyware and malware can also interfere with the network connection and prevent the computer from connecting to another computer or server.
Quick Fixes
Check the LAN cables running from the computer to the modem. Damaged cables and loose connections can prevent an outgoing connection. If the computer used dial-up previously, disable the dial-up properties in the Internet Options pane from the Control Panel. Open the “Connections” tab and tick the box for “Never dial a connection.” Then, open a Run box, type “ncpa.cpl” (without quotes) and press 'Enter' to enable the network adapters. Right-click on “Local Area Connection” and check “Enable.”
Resetting
Resetting the modem forces the device to rewrite its connection settings. Disconnect the cable that runs from the modem to the computer and turn off the modem for at least two minutes. Turn the modem back on and wait until it detects an incoming signal. Reconnect the cable to the computer and test the connection to see if the 678 error is resolved.
Reinstalling
Drivers can be corrupted by malware, software bugs and, occasionally, software updates. Open Device Manager and expand the “Network Adapters” list. Uninstall all of the network adapters listed there. Reboot the computer and let Windows scan for new hardware. Once the network adapters are found, Windows will reinstall the drivers. If no drivers are found, you’ll need to download drivers for the devices.
Repairing
Rewritten Winsock and TCP/IP settings could cause connection headaches. Type “netsh winsock reset” in the Run box and press 'Enter' to reset the settings. The command prompt window will flash when the computer processes the command. Reboot the computer and try connecting to the Internet. Note that certain security programs that monitor the Internet, such as anti-virus applications, may not work properly after the Winsock and TCP/IP settings have been repaired. Reinstall the security application to remedy this problem.