Was your router's firewall not always enabled? You could try disabling it & see what happens... just as a test. You can always enable it again, right?

I'm really not a router person, so I have very little knowledge of these devices! As for other p2p, I only use LW & FrostWire (pretty much the same).

Installing an older LW version isn't going to help I'm afraid. Has this problem literally happened overnight? I really would suggest that you at least call your ISP & make sure that no p2p blocking is going on. If only to rule it out as a cause of your problems

But first, just try shutting off that router firewall... if the firewall icon goes away, that's great but if you still can't connect... I'd be interested to see.