Help with icon thumbnails!

[TalesInc]

Ok i guess many ppl may have had the same problem. My video thumbnails for all VLC related files. (files which cannot be played by wmv). They are all gone!. And also almost all .mp4 .mkv .mpg, all formats with m have all their icon thumbnails taken away. and everytime i open my folder with the videos in it, it lags for a moment. Just like its actually seeking for thumnails to display on the icons when the files are first created. And it's realli getting on my nerves that it always lags when i browse my folders. help me pls! I dunnoe wad happened. One day when I woke up the thumbs just disappeared.