Sometimes hardware devices in Windows 7 are completely hidden in Windows 7. For example, I had a VMWare Windows 7 guest OS running on an ESXi 5.1 server and I did an 'upgrade virtual hardware' step. When I booted up the guest OS, the network connection was called "LAN connection 2" instead of just "LAN connection". Apparently Windows now saw a new network interface card, but the old one was still somehow hidden in the system. Opening up Device Manager in Windows and going to "View > Show hidden devices" STILL would not show the device. But I knew the old one was there because when I tried to rename "LAN connection 2" to "LAN connection" it would complain that that name already existed - but it was not visible anywhere. Then I found this solution:

Open a command line window and type the following two lines:

set devmgr_show_nonpresent_devices=1
start devmgmt.msc

Now the Device Manager shows up, but now when I click "View > Show hidden devices" it does indeed list the hidden network device. It shows up as a 'dimmed' entry in the list that I can just click and select the uninstall option on. After that, I was able to rename my network connection back to its original name and reset the IP address settings without getting complaints about the name or about another network card already having those IP settings.