Can't watch any video after exporting, but can see them in new project

Hey

I was recently animating some logos with after effects, but after exporting them with the media encoder I found that I couldn't view them; if I click to open them it simply has the windows media player logo and the length of the clip, but if I click play nothing happens. However, if I place that file into premiere pro then it looks as though it has exported perfectly - until I export it from premiere pro (not the media encoder) when it stops showing up again. So, I can't play the file as normal, but I can view it when I put it into another project.

I spoke to the colleague whose computer I was borrowing (it's the only one that supports adobe programs so we both use it) and the same thing has apparently been happening to her no matter how she exports - quicktime, mp4, etc...

Any help with this issue would be greatly appreciated!!

Thank you!!