In the past I have been using Zoom player, but because of some glitches I uninstalled it and replaced it with Media Player Classic.
During the installation it asked me to uninstall the video codecs in my pc to prevent conflicts with MPC (true or not I don't know) so I did.
All the video files that I've been playing since then have worked perfectly. The only problem is that I now want to edit some video, something easy and simple without any frills, just take some parts of a movie out. To do this I used MS moviemaker but I was not able to do so because it told me that the codecs to process that video files are missing.
Is there a video editing soft, perhaps freeware, out there which includes video codecs? Or do I need to re-install the video codecs to edit video, and will this not mess up my system?

You should be able to down load the codec pack from divx.com this may enable you to do what you want. It will not mess up your system.

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Every thing said by me should be taken with a pinch of salt. Unless you have high blood pressure, then I would recommend a salt substitute.