Those machines are different LANs so you need to talk to who set this up to create a single LAN.
I just got a 2nd computer. A laptop running Win8. I also have a 1 year old desktop running Win7 that is hard-wired to my Verizon FIOS wireless router.
The two computers can't see each other on the homegroup network. I've turned on all the network discovery, etc. The laptop can see the router and get to the internet and see the printer that is hard wired to the router.
I think I may have found the issue, but don't know how to fix it: The desktop has an IP address of 192.168.2.100, but the laptop has an IP of 192.168.1.10. I am thinking that the 3rd string of numbers needs to be the same (???), but don't know how to get that to happen. I tried setting a static IP address on each of the computers, but when I do that, neither of them can see the router anymore, so they don't see any network and can't get to the internet.
I need the computers to see each other for file sharing, and because I have a laser jet printer connected to the desktop that I want to be able to use from the laptop, but it's not a "network" printer, so I'd need to set up print sharing.
All of this stuff was working back before my old laptop died a few years ago.
Also, as additional info, I have a VOIPO (VOIP) router and a DirecTv router wired into the wireless router. I asked on the VOIP forum if their router has any effect, but it doesn't. Don't know if the DirecTv router is an issue or not, and don't know how to find out.