the problem lies with "files association" ...
go into your TCPMP settings and check/uncheck file extensions that you want/not want it to open with ...etc
can't say the same for windows media player though !!! ... I hate it with a passion ... crappy video size ... what's with the NO PLAYLIST ??? and it won't play AVI
... and on and on ...etc !!
there are way better 3rd party softwares for your medias !!!
TCPMP is the most versatile ... but not much on the GUI ... best of all .. it is FREE
Conduits PocketPlayer is great ... but it's not free