Something about Windows Media Center I need to know......

I've got a lot of pictures and music on my system (the pictures are mostly
all .jpg's and the music is mostly all mp4's) that do not want to
display/and or play correctly when I'm using my extender downstairs. All
pics display ok while on my desktop when using Windows Photo Gallery, but
they will NOT display when using WMC neither on my desktop or via the
extender for the big screen downstairs. Also, NONE of the mp4's will play
either. I'm assuming that maybe there needs to be some sort of conversion
for the mp4's to wmv or something? Any help with that would be welcomes
greatly. In other words, do they really need converted, and if so, what is
the best program to do it. Concerning WMC via the extender, why do the
jpg's display ok on the desktop, but not on the big screen downstairs via
the extender? The system shows only some of the directories, and the ones
it does show are labeled as empty. I would greatly appreciate ANY
help/ideas here. Thank you for your time.