Why did MSN Messenger stop alerting me to new messages?
Did you upgrade messenger lately? Then it’s probably because it thought you were busy doing something important, like playing a game.
At least that’s what happened to me.
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A new option appeared in version 6, I believe, in Tools->Options->Personal labled “Show me as Busy and block my alerts when I’m running a full-screen program, such as a slide presentation”. I’ve also experienced this running a game or a Remote Desktop client session.
And it apparently defaults to “on”. Turn that off, and you should be getting those all important instant messages interrupting you once again.