Installed IE8 --foolishly when 7 was working fine--and now I do not have any audio anywhere and many other problems

I had a bad enough time going to Vista, but now, I stupidly thought IE 8 would be nice, and since then, start up crashes, NO audio anywhere--my Windows icon is even gone...can't participate in Webinars, or hear audio on powerpoints.  This is currently the biggest problem and I need help quickly--I would appreciate your help.  I am a middle experienced user, but can follow good directions.  Except to leave well-enough alone.