do you by any chance have dual monitors or had dual monitors? if for some reason it's open outside the main screen, it could be active but hidden.
if it's not even in the task tray, then you might have a bigger problem. try in safe mode, try removing msn from your startup and open it yourself when your computer is completely booted up. check your anti-virus, anti-spyware, firewall, etc... see if any of those is blocking anything. it might be good to dissable EVERYTHING you can and then try to open msn. give us some update if you get it working!
|