Avast doesn't have a firewall currently, although the V5 suite will.
Are you sure that your port forwards are pointing to the correct IP addresses?
If you are trying to port forward through the wireless router, so you'll be double NAT-ing.
What I do in this situation, is set a static IP address of the second (wireless router), forward all ports that I need in the first router to the second router. Then, on the second router, forward all ports to the host(s).
Of course, if you could omit one router, it would be a lot easier...
Internet (some IP address) ===> Modem ===> Router1 (10.1.10.1) =====> Router2 (192.168.1.1)
forwardR1 (80) => (192.168.1.1) forwardR2 (80) => (192.168.1.5)