Windows XP:
Start -> Control Panel -> Network Connections
Right click the one that says "Microsoft Loopback Adapter" as the adapter name and press "Disable".
Repeat to enable it.
Windows Vista:
Task Tray -> Right click the little computer -> Network and sharing center -> Manage Network Connections
Right click the one that says "Microsoft Loopback Adapter" as the adapter name and press "Disable".
Repeat to enable it.
Windows 7:
Task Tray -> Right click the little computer -> Network and sharing center -> Change Adapter Settings
Right click the one that says "Microsoft Loopback Adapter" as the adapter name and press "Disable".
Repeat to enable it.
