Firstly, Sitecom is one of the few brands with which I am really not very familiar; could you post a link to your model's pdf manual please?
Secondly, have you configured your client (software) firewalls yet? They need to have permissions created to allow two-way trusted traffic through the LAN adapter (with a range of IP addresses to allow for dynamic IP assignment) unless these rules have been created automatically. If so, they need to be checked in detail - I'm not at all keen on automatic rule creation because the firewall can sometimes get it wrong.
We often have to talk about firewalls around here because it is one of the most common issues that people can neglect. As I always say; you need to know your client firewalls (and your router, ideally) inside out to get the most out of them. If in doubt, do not use a firewall until the network is sorted. That way, it's one step at a time.