Computer problems

Computers...you gotta love 'em or hate 'em. Well, not really but after upgrading my five your old Dell Dimension 8200 from Windows 2000 Professional to XP Professional, I am about ready to pull my hair out or go mad or both. The transition worked fine except for one thing. Sounds do not work as they should. The sound card is OK because log-on and log-off sounds play, my music files play, videos people send me which are played via the Windows Media Player have sound, BUT, if I view a media website and there is a news story imbedded there, the sound will not play even though I can view the video. Also, mail notification sounds and some other system sounds do not play. E-cards sent to me will not have any sound either even though it is supposed to be there. Oh, by the way, those computer system sounds that won't play when they should, can be played manually if I open the Media folder and click on them. So what in the world is going on here Mr. Gates??? Anybody??? And to make matters worse my old sound card and its drivers are no longer support by Santa Cruz Turtle Beach. I just wish I could remember what I did earlier this week that had everything working as it should for a few hours.