'Advanced' is greyed out too!!!
I've reviewed the HijackThis log again, I still can't say that I can see anything else that stands out immediately although I now I'd be looking at other software on the PC.
I did notice the Bonjour service (iTunes and other) zero configuration service, I don't think this would normally cause a problem, but given we can't find any other source I'd look at this next.
There's some potentially useful information here too http://support.microsoft.com/kb/923737