Why does Yahoo Messenger 7.0 sign me out?

I am not doing anything and I don't get a message of any kind Yahoo messenger will just sign me out then right back in I have version 7 and DSL thru SBC and it is SBC yahoo messenger I can upgrade from this version because version8 gave me to many problems I ahve uninstalled and reinstalled several different times and it doesn't fix the problem is the problem with my computer or yahoo it's self plz help if you can?