ill assume you have forwarded the correct dcc ports you have set in mirc to the correct ip of the pc
One thing to check is you dont have 2 layers of routers, ie: a VOIP router then your lan router? if so you need to forward from the viop router to the lan router.
To check your firewall you can go here
https://www.grc.com/x/ne.dll?bh0bkyd2 if there STEALTH there likely blocked, anything else means there not blocked (but maybe nothings responding on them, which is ok)
I have not setup a McAfee firewall, but as well as allowing mirc in and out, you may have to pinhole the dcc ports them selfs to pass through the firewall, since when sending files you tell the reciever your ip:port over IRC and then the reciever actually contacts to you directly ip to ip:port and thus you need to allow inbound (apparently to the firewall) unsolicited conenctions.
Since you are behind a router, you could with a resonable saftey margin shut down your firewall to test if it is the thing that is blocking you, then if it is raise it again and sort out how to allow the ports through (see above for some help maybe). Of course mayeb its a port forwarding problem still & a firewall problem, so always consider theres more than one blockage in place.
