problems runing video clips from digital camera

I am runing on windows xp and I used to be able to
download still digitial pictures and short video clips on
my pc and they would function normally, recently I am
only able to hear the sound from the video clips but can
not see it. I must have deleted a file while clearing out
some old stuff. Can anyone advise what to do? is there a
dignostic tool to help or is there a file i can download?

Regards