MPEG files no longer recognised by computer - says it is not a movie file

Can anyone give me any pointers?
I was browsing my photo/video files and anything that I have downloaded from my camcorder is no longer recognised as a movie by my computer.

Any movies created by my two cameras are still recognised. The default player for the camcorder movies is windows media player and this says “not a video”. If I try to play it through real player it says only part of the file can be played and plays the sound.

Does anyone have any clues?

Many thanks

Sarah

PS - am relative technological dunderhead so please go easy!

A few questions: what make and model is the camcorder? Have you recently installed or uninstalled anything before everything stopped working? Finally, what is the format of the videos produced by the camcorder? (I would guess MPEG-2, but to be sure, you should feed the file into a diagnostic utility like gspot (http://www.headbands.com/gspot) or avicodec (http://avicodec.duby.info))

Hey - sorry for not responding but I wasn’t familiar witht he format of the site - kept checking but didn’t realise you had responded. Turned out my partner had deleted something he thought wouldn;t make any difference, but it did! Thanks for your help! :- )