Have you tried reinstalling it?
If you want to try out other software however, i can recommend you is Digsby or Trillian. Both are multi-client IMs (meaning they can chat with other IMs such as AIM, MSN and MySpace). I been using Digsby and love it alot. You can not onyl chat with multiple IM clients, you can also get notifications of your myspace and facebook updates, twitter updates and e-mail. It's basically social networking straight from your desktop. IMs include facebook, myspace, msn, AIM and etc.
I just visited the trillian website and looks like you can do the same thing. so whichever one you want to go with is up to you.
Digsby -
http://www.digsby.com/
Trillian -
http://www.trillian.im/
If you like the group chatting and custom smileys then I'd go with trillian. I never used it so im not sure about the smileys, but I think you can.
Digsbay can't start group chats but your friends can invite you to group chat. You are also stuck with the smileys digsby has. However, digsby is still being developed more and hopefully will get more neat features. Which ever one you want to choose is up to you.
You can also try out these other alternate multi protocol chat IMs:
http://www.pidgin.im/
http://www.miranda-im.org/
These are just msn clones if you just want msn:
http://www.emesene.org/
http://www.amsn-project.net/index.php
You cann also try out these web based IMs, they are also multi-protocol IM software like digsby and trillian:
http://www.ebuddy.com/
http://www.meebo.com/
All of the above will get you connected back with chattin with your msn buddies, so pick the one you like the best and that will work with your pc.