I concur with Dignan.
I recently also experienced weird network problems, and, after much fiddling with it, could track the issue down to the driver of the network card. In my case, it's a real Intel onboard network chip, but I let it use the Windows driver that got installed when the OS was. Everything worked then, but network speed did not come above 9 MB/s and sometimes locked up too, even though the system insisted the connection was a Gigabit connection. As a last resort kind of thing, I eventually installed the real Intel NIC card drivers and that magically worked!

Maybe that Windows update did something with the NIC card driver? It's worth checking out.