hi all, hope u can help

i'm using an s-video cable from my desktop pc to my tv (which is in another room) to watch movies etc (AVI format).
everything works fine apart from some movies, which do not appear, but only on the tv. when i open the movie on the pc, they play fine, but when i walk into the other room, the area of the screen where the movie is playing on the pc is blank on the tv.
at first i THOUGHT it was because the videos could be copyrighted or protected, but then i realised it can't be this, as my own home-made movies (also AVI format) play back with the same problem, and i KNOW that they aren't copyrighted or protected, as i recorded them myself. I have some other home-made movies on my pc which are in ASF format and they play with no problems, i get the movie at both ends.
I have tried using vlc player, media player, and winamp to play the movies, all of which give the same result. I'm guessing now that its probably some sort of codec issue, but i could be wrong.

here's my system specs...

intel p4 2.26ghz processor
512mb rdram
256mb nvidia geforce 5700le graphics card (agp)
1x80gb hard disk
1x200gb hard disk
1xdvd-rw
1xcd-rw
windows xp home EDITION (SERVICE pack 2)

thanks for taking the time to read this :-)

funkyspaceman