Cannot get video clips to play in Window Media Player

Hi.
I’m having a lot of trouble trying to get some Handycam clips to play in WMP after I’ve strung them together in WIndows Movie Maker. I’ve tried downloading codecs and I have downloaded DivX Plus and I’ve downloaded G-Spot all to no avail. Every time I just get a black screen and the audio sound. Please help (and put it in layman’s terms)!