network homegroup won't connect

Are all computers on the same subnet (ie: 192.168.0.xxx)? If it works when wired, but not when wireless, then I'd look at the NIC settings on the wifi card to make sure you are getting an IP assigned by the router.

Network and Sharing Center -> Change adapter settings -> right click on the wireless network connection, and select properties -> click on TCP/IPv4, select properties

You should have obtain ip address automatically selected, and obtain DNS server address automatically selected.

To get the current IP address on a computer, open a command prompt (hit your windows key on the keyboard and type cmd, then hit enter) and type "ipconfig /all" without the quotes. I'd do that when connected wired and then again when you are connected wireless, and see if there is a difference in IP addresses.