I donno why whenever i play wmv files, the playback become laggy.

If you are using Windows Media Player, try updating it, or try downloading WinAmp to see if that works for ya. I would also make sure you have the latest drivers for your soundcard as well. Which ever player you end up using, go to the preferences and make it the default player for that type of file. Sometimes drivers get corrupted by other applications so find one player you like and uninstall the one that doesn't work. Then run disk clean-up and a defrag, it cant hurt.

I previously use ffshow as codec for avi file, but suddenly after windows update, playing avi files become slow and laggy. So i change to k-lite codec. After installing it, avi files can be watch with no problem but now WMV files become slow and laggy with windows media player.

Diskcleanup and defrag don help much. Maybe its registry to set .wmv to use the default codec. So how to edit the registry ??

HEY affter i run the defragment, My HDD started to be noisy. what to do??

I cant think of a reason why would defragging make a disk noisier...
It would be more logical to make it quieter, as the data gets more organized.

But, about your video problem - try playing the files in VLC player.
Go here:
http://www.videolan.org/vlc/

and download the latest Windows version, then report back.