Before trying to re-install MSN Messenger open up IE and then go to Tools -> Internet Options -> General -> Delete Files -> select Delete All offline Content and then select OK and then OK.
Then, go to explorer and delete the MSN Messenger folder typically located in C:\Program Files\MSN Messenger. Re-boot your computer and then go to the MSN Messenger Download Site and re-download the latest Messenger. Do not choose to open it - instead download the entire program to your desktop as pictured below;
You should now have a completely removed MSN Messenger program, a cleared out Internet cache and a new download of the MSN Messenger program on your desktop. It's important to have followed the steps above in the proper order as outlined.
Now install the new Messenger by clicking on the icon and following the on-screen prompts and then re-start and re-try to see if the issue is gone.
If the issue persists then please visit Windows Update and ensure that all updates are installed for your operating system. If you find some that were not installed please install them and then re-start your computer and re-check for MSN Messenger functionality.
If this doesn't work, check:
http://computer-help-tips.blogspot.com/2011/05/i-cannot-sign-into-msn-messenger.html
