Hi and welcome to the forums
If you can ping the router then the connections on all the computers are sound.
In this sense the network is established.
The fact that you cannot ping from one computer to another computer suggests a firewall issue.
Likely McAfee is blocking your pings on the incoming computer.
To be sure of this, either temporarily disable McAfee Firewall or check your network settings. Usually setting your local network as being "trusted" or "safe" allows pings to work properly.
Unfortunately I don't use McAfee so can't offer any more specific advice.
Be assured though that the fact you can ping the router from each computer means that they are all connected and so networking will be easily possible once your firewall is correctly configured on each machine.
For file sharing, in Windows, just make sure that all the computers are using the same workgroup name. That way, with your firewall set up corectly, your computers will be able to discover each other with great ease through My Network Places/Network Neighbourhood.
Also games sharing should be very easy.
Your router does not restrict traffic between LAN computers, so no configuration changes in the router are necessary.
Once again the stumbling block will be your firewall software on each computer. Provided your firewall is properly configured, gaming between your PCs will be hassle free.