Cannot establish new TCP connections.

Help please!

I am having a nightmare of a problem with Vista Bussiness. The symptoms are
as follows:

Suddenly I am not able to browse the Internet. I get an instant error
telling me that the page I am trying to view is unavailable or something
along those lines. This is a systemwide problem (it happens with both FF and
IE). Furthermore I cannot initiate any new connections at all. I have tried
using telnet to servers (both local and external) on ports which I know to be
accepting connections. I have triede disabling/enabling the network
connection, to no effect. Sometimes the error will "go away" by itself, in a
matter of minutes. But just as often the only resolution seems to be a reboot
of the system.

I have a sneaking suspicion that these problems are connected to the TCP
connection limit, often I will get a warning that the TCP have reached the
connection limit, according to the Windows System Logs.

Therefore I have also tried doing a "netstat -no" in the CMD shell. To see
if I could find a process which has a lot of waiting TCP connection. But
alas, no help there either. The only connections showing up are the standard
listening ones, but no waiting ones whatsoever.

Now here the strangest part. This happens regardless of which NIC I am using
and regardless of which network I am on. I have experienced this problem, on
the same laptop mind you, both at home, when I am using my private WIFI and
at work where I use a wired connection.

So I guess we can exclude any hardware issues. And so it must be down to
some setting or perhaps a bug in Vista.

Any help would be highly appreciated.