I have a windows 8.1 machine that is wired to an ASUS router. I have a few other Window's 7 machines that are connected via Wifi.
The Wired 8.1 machine can not view any of the Wifi machines in the Network view. Also, the Network map does not show them. Can't ping either.
The Wireless Windows 7 machines can see all Wifi machines as well as the 8.1 machine. However, the Network Map shows the 8.1 machine having a direct connection to the router icon. The Windows 7 machine has a question mark between it and the router.
Also, I had a Homegroup setup but the Windows 8.1 could not view it. I deleted the homegroup on the Windows 7 machines and started a new one on the Windows 8.1. The windows 7 machines are asked to join that homegroup but are denied because it states the password is not correct. However, the password is correct. I have even changed the password to something very simple and tried again. Something seems to be blocked the communication.
Windows Security Essentials on the Windows 7 machines. Defender on the Windows 8.
Hopefully, this can be followed.