Internet Connection Problem

[Michel007]

I've been having strange connection problems on both pc's connected to the internet. I've had a router (D-link DI 704UP) for about a month now, but the problems popped up just recently. Some applications, like steam and some p2p programs do not connect. I can get online just fine, download things and do things as normally but any program that needs to connect on startup seems to say it's behind a firewall. I disconnected the router and went direct to modem, but that fixed nothing. All p2p programs are experiencing same connection problems, on both computers.

Can someone clarify? and how to solve this issue?

Thanks in advance and please quick reply!!!!