Not sure if I can help completely. I have a laptop running Windows 7 connected wirelessly, a PC running Windows 8 connected wirelessly and a NAS wired to my router and my SMP is also wired to the router.
One thing I had to do was make sure they were all on the same ‘homegroup’ which you’ve done but also having the same user name and password.
Double check your username and password in SMP settings and make sure it’s the same as your Windows user name and password. Also make sure UPNP is enabled on your router.
Doing this I have no problem seeing anything.