Like I said, I'm running the latest version of LW for Mac. I guess that should be 5.5.13

And well, off course I could post details like the ram of my MacBook, but I highly doubt that'll help. The same client works perfectly fine when I visit a friend, and it used to work in my own house as well. I've had an interim tenant in my house, but since he neither had acess to my MacBook nor to my router (well he was from india so you'll never know, but at least he shouldn't have had) that damn program should work exactly the way it used to before the interim tenant was here.
My "firewall" is LittleSnitch as it always was, yes Limewire is allowed in there. My provider is a german provider and definately not blocking me since he isn't allowed to do so. And just like I said - everything is configured the way it always worked. Except that the configuration status in Limewire keeps telling me that the connection is building up right now and never finishes.