After reading Per's comment, I realized that I performed several Microsoft Updates and upgrading my Avast anti-virus. It is possible that either change caused some conflict. After some frustrating hours of tweeking, I decided to do it the hard way. Since I have a Microsoft Technet Subscription, I downloaded Vista Ultimate SP2 and did an "upgrade." My computer went through several more hours of purgatory, then bit after midnight, Vista screen popped up and now XX plays again! It seem the problem lies with Vista OS.
BTW, Vista now loads faster, but still scratching my head as to what went wrong.
Per and Peter, thanks for your help.