Try downloading the most up-to-date MSN Messenger (Live) from http://www.msn.com/
(yes, you'll have to go into the Messenger section) and install it (while making sure you have closed out your MSN Messenger so that it doesn't even appear in the system tray).
Next, open up Internet Explorer and go to http://windowsupdate.microsoft.com/
- go to the custom update and install everything that you can see (after waiting for some results to pop up).
Restart your computer. If your symptoms do not change, although this is rare for it to affect a messenger, you might have some odd spyware, adware, or malware. Who knows, let's assume you have all of it. Make sure you have Spybot - Search & Destroy and AdAware (the latest version downloads can be found in a stickey in this forum). Next, make sure you update both of them as much as possible. Do a full, complete, deep scan (no quick or smart scans). Then remove any malicious jazz the scans find. Remember, do not run both programs at once. It's best to run one, remove it's findings, then run the other, and remove those findings as well.
Then restart your computer.
By now, it should
be fixed if it was caused by out-dated software or (for some reason) some kind of malware. If the issue is not resolved by the time you have done all this, come back and slap me in the face. I'll see what else I can think of...