When you start MSN after a while your computer freezes to a point where even ctrl alt del doesn't work tried reinstalling my system to figure out if it may be another program but that's not it help?

I have the same problem. I have Windows Live Messenger verion 2009 build 10.0.8064.206. I tried to downgrade it to 7.5 but it didn't work because I have Vista. I don'y know what to do. I need to run my messenger but it is freezing my ystem