messenger7.0

I was running the 6.2 version of messenger and then I thoguht ok let's
upgrade so I tried to download the 7.0 version. it seemed to download fine
and all with the icon in my toolbar but it will not open at all. I am trying
to get it to work so I can keep in touch with my 13 year old son in MN.
anyone have any idea's as to why this isn't working?? PLease help