Wide World of Women

Out of nowhere my videos stopped playing in Windows Media Player and I only get sound. Most show a static photo of a frame from my video while some others show the default windows media player icon. In both cases the sound plays normally but no moving video!
All the videos play perfectly (both video and sound) in Windows Media Center, however I'd much prefer them to play in the default player like they used to. I did some research online and tried a couple things, but nothing worked and I am hesitant to download codecs that may be harmful. Any help or guidance would be appreciated. Thanks!

My info:
MS Windows7 Home Premium 64-bit SP1
Using Windows Media Player Version: 12.0.7601.18150

I'll get the simple questions out the way first:

1. What format are the videos you're trying to play?
2. Have you tried VLC? It plays nearly everything.

In any case, I'd always advise using VLC and avoid installing codecs to make Media Player work.