Digital camera video not playing in WMP 10   

I have just acquired a Praktica DCZ6VR digital camera. It has a facility to 
take videos as do most digital cameras nowadays. So if I make a short video, 
I can replay it's okay on my camera, but when I remove the memory card and 
load the files onto my computer, it saves it as a Windows media player file, 
which is correct. When I try to play the file, using Windows media player 10, 
it does not play back the file, but it does go through all the correct 
motions, with the slider at the bottom of the picture moving to the right as 
if it was playing the file, but the screen remains black. It is the same when 
using real player. I can play DVDs ok on my computer using windows media 
player 10.
 I have tried the videos on a couple of other people's computers, and they 
work fine on their computers, one has Windows media player 9 installed, and 
the other has Windows media player 10 installed. I tried reinstalling the 
operating system, (Windows XP professional) on my computer, and with the 
reinstalled operating system, then it will play the file correctly, using my 
Windows media player 10. I have Norton ghost installed so I can return to my 
regular setup..... no problem. 
I have Windows XP professional. 1.5GB Ram 2.7GB processor. 
Does anybody have any ideas what the problem is please?

date: Mon, 14 Apr 2008 05:43:00 -0700   author:   mel