Great answer, Shortstuff
I've perused both your posts real carefully looking for some obvious clue, but nothing jumps out and hits me.
I asked about other voice programs not so much thinking of conflicts, but just feeling it would be helpful to know if it's only Yahoo that doesn't like you or whether in fact it's simply using voice over internet, regardless of the actual program. Oh well, no matter.
I see you have a lot of music programs - perhaps one of them is causing a blockage? I'd suggest perhaps after a fresh reboot close EVERY other program you can see - and even do Task Manager and End Task on everything in Applications, and THEN try loading/running YM.
And Norton Security Suite - I've no experience of that but I've read a few posters who have problems with THAT and YM. Is it possible to close/disable that (just temporarily, for a few minutes) then see if YM behaves for you ?
But I hope some others might offer suggestions too from all you've described - good luck with the ongoing mission.