I find that pointing the browser to
www.bbc.co.uk normally kick starts the registration process, just make sure that in Internet Explorer, tools, Internet options, connection, you have selected "Never dial a connection" before trying to point the browser anywhere. Also check under "File" in the menu to make sure you are not browsing offline.
Did you install the CD and then it crash or did it crash prior to installing?
One thing to check is that the STB is enabled for Broadband, you can do this via the remote control, press Page up, page down and then the blue button. You should scroll across a couple of screen and then get to one with a QOS file, bronze,silver or gold. If it states no QOS then it's not enabled.