Lies your problem. I know, I haven't used MSN or similar connections before, but they (and Hotmail) tend to leave your system open to all sorts of nasties, viruses, worms and the like.
I had a problem a while ago like that, I changed the ISP home page in Windows XP to my ISP's home page, it was promply changed back to MSN!
What I did, was, after much messing about was back up ALL my irreplaceable data - e-mails, other data files and downloads, then completely re-load Windows XP Home Edition, re-formatting along the way, that cured it.
If you want, have a look at this link, it may help http://reviews.cnet.com/5208-7813-0.html?forumID=5&threadID=124775&messageID=1412967
Microsoft Windows XP
service Pack 2
CPU 230 GHz
2.29 GHz, 248 MB of Ram
When I get connected, I can't get my homepage, get error msg. "page cannot be displayed, cannot find server, and at the bottom, it says "Unknown error."
This has happened for a year, I usually have to connect through blogger or MSN.