It sounds as if the problem may lie in your router, and quite a bit is explained here for various Linskys models.The thread concerns Limewire, but obviously is relevant
http://www.gnutellaforums.com/showth...516#post179516
In the last post is also a link to portforward.com. See if this helps. If you are not connected to any other Ups/leaves but you have already established existing connections, those connections will continue in certain circumstances.
do you see nothing atall trying to connect in the connections window? Often it takes quite a long time for "connecting" to turn to connected
Let us know if this helps for now. I must rush, but let us know how you get on and if you need more help.
Rebooting my comp cured this problem on one occasion btw, but I don't have a router that could have caused it