Networking has never been Windows’ strong suit, especially for home users. With Windows 7, Microsoft introduced a new feature called HomeGroup that should (in theory) make home networking easier. You just go through a dead-simple wizard and are given a password. Go to other Windows 7 (or later) computers on your network and go to Control Panel > Network and Sharing Center > Homegroup > Join Homegroup and enter the password. Done… at least in theory.
But the HomeGroup applet doesn’t have a simple “delete this network” or “reset this network” option. If you create a HomeGroup on one computer and that computer later goes away – via upgrade or hard drive crash or the standard wipe and reinstall – you’ll still see the ghost of the old computer on your network: if you try to create a new HomeGroup, you’ll get the following message: “[user] has already created a HomeGroup on [old computer]. Do you want to join it?” Of course, the old computer is gone, so you can’t join the HomeGroup. If you go to a different computer still connected to the HomeGroup, you can only leave the HomeGroup, not create a new one or get rid of the old one.
So how you can you get rid of an old HomeGroup? It’s simple, if not the first thing you might think of: fully shut down all the computers you want in the HomeGroup (sleeping or hibernating them won’t cut it; you have to shut them down fully). Then power on the computer you want to use to create the new HomeGroup. With all the other computers off, you should be presented with the “Create HomeGroup” option: