I was watching tv on media center when the tower made a buzzing sound and then the screen went blue.  System froze so I shut it down. Turned it back on but very slow.  Called Dell and they had me check the hard drive and fan...ok. I tried recording on media center and video is choppy and freezes.  My hubby went and got an external hard drive and put media center to that to see if that would help.  It records to it but video and audio is still choppy and recordings now stop for no reason. The tv I recorded before the buzzing is fine.  The Dell rep wanted me to do a system restore since I have the external hard drive and he was very pushy about that would solve my problem.  I told him I would wait since he only checked two things.  He said it could be a software problem also.  I also did a system defrag which helped with the speed but not with media center. Any suggestions?

 Dimension 5100 windows xp media center