doesn't open correctly/ doesn't play

Dear all,

I am trying to open/play downloaded tv episodes (extension .avi) with
windows media player. However, sometimes the media player opens, but does not
play the episode, and sometimes it doesn't load at all. I have tried checking
for updates, but it says there are no important updates. I have tried
downloading version 11 (I am not sure which one I have, and don't know where
to find this), but it says I already have a more recent version on my
computer. I can't seem to find windows media player in my 'programs' section
in windows to uninstall and then re-install to make sure there aren't any
problems.

What do I do?
Thanks,
Saskia