1) Do you have anti-spyware?
2) If you can still use your Internet Explorer or Firefox, go
download one from http://www.download.com
3) I suggest Ad-aware by Lavasoft. After installation, update the
definition file.
4) Scan your computer for spyware and delete them all.
5) Reboot your computer
6) I hope you are able to log on to MSN now.
Else, could be your Internet Explorer settings or Firewall.