This is an old problem and dates back to at least XP, but probably existed in NT 3.1.
You need to make sure each system has a matching username and password. So for example say your Windows 7 system has a user account named "bob" with a password of "smith". You need a u/p combo of bob/smith on the Windows 8 system. There are other ways to do this, but that is by far the easiest. The whole homegroup thing is supposed to make this process easier, but I'll have to agree they didn't just miss the mark, you can't even see where the mark is from the homegroup.
You can also disable the Windows firewall on both if you have a router. While there's an argument to be made that protection only at the gateway isn't enough, for a home network it is probably sufficient. The AV program wouldn't have anything at all to do with this, so you can disable it or enable it all you want, it won't change anything.
I am trying to get a Windows 7 Pro machine to communicate (share files) with my Windows 8.1 Pro laptop. This is a private small home network.
This used to be easy. Why is ms making this a nightmare now. It just won't work no matter what I do. I can see the names of each computer on each machine, but apparently the Windows 7 machine is "denying" access.
I disabled Avast on the Windows 7 machine. Another message says "Windows can't communicate with the device or resource". I've been trying to troubleshoot this every which way I can, and ms provides no REAL clues whatsoever.