Hi Lucy,
I dont think this is a problem with MSN Messenger. One of the things that you can try is System Restore.
Start>>All Programs>>Accessories>>System Tools>>System Restore.
This will allow you to roll back your computer to a previous date when you think that it was working ok. Any programs that have been installed/unisntalled between the date you select and today will be modified as to how it was on the selected date. However, personal files will not be affected. If it turns worse, dont worry, because you can undo the last restoration. Try it and let us know how it went
Kash, April 2006