Video display has suddenly become slow

Hello Friends,
All of a sudden any kind of videos, of any format and run on any player have become slow on my Windows XP machine. I used to able to run two movies on my Dell Laptop but now even when I run one movie the movie stalls. I can see my CPU peaks to 90-100% and then the movies starts to stall. However, the player itself is only using 50% of the CPU the rest is used by 'System' process. If i pause the movie the CPU usage goes down and then after some time of resuming it will go up again to 100% and start stalling. My memory is less than 20% used and there is no disk trashing? Any solutions, this issue occurs with all media players, FLVPlayer, Windows Media Player, Quicktime player.