System lagging

Since a few weeks, once in a while my system is start lagging when im watching a video (xvid). I tried with WMP10/WMP7.2 or Powerdvd even bs player...Update my video/audio driver...also have the lasted version of the xvid codec... If im opening my task manager i have a process call "system" which will take like 20-30% of the cpu. I check my cpu temp (50deg) and my MB temp (30deg).


P4 3.2 540
Asus P5AD2-Deluxe
1gb DDR2 533 dual
Ati X700 256 pro PCIX
2xraptor 37gb
4x300gb maxtor 16mb
Zalman fan