Vista ICS and XBox 360

Hi,

I'm trying to use ICS to connect to my 360 so I can use XBox Live. I have
my console connected to my ethernet card in my computer through a CAT5 cable,
and my PC is connected to a USB cable modem. Obviously, my PC connects to
the internet just fine. The console is another story. Earlier today, it
worked just fine for a while, then it suddenly disconnected itself for no
apparent reason. I looked at the XBox support site, which suggested power
cycling my network components, so I did that, and now the console refuses to
connect at all, failing the IP test every time. I have tried setting the
console's IP address, subnet mask, DNS, and MAC address manually, all to no
avail. I have since reset everything to automatic. According to the XBox
support site, all of my settings are correct, yet no joy, and for some
reason, they don't respond to e-mail support requests. Can anybody help?
Thanks.