problems with mpegs

I don't know how this happened but I can not play some mpeg files. I can't remember when this happened but it wasn't always like this. For example, I recently downloaded the Aspen Brock mpeg files just posted today and combined them. But when I tried to play them all I got was the first 3 seconds even though the file was recorded as being over 30 megabytes. This happens with essentially all mpeg files I download (whether they have to be joined or not).

Does anyone have an idea why this happens.

Thanks in advance.