NO VIDEO CODEC WORKS

Ok ive pretty much have had it with trying to figure out how to get videos to work... ive tried diagnosing things with gspot video inspector radlight... a bunch of different programs ive tried installing NIMO unregistering conflicting files... but now nothing works, Ive just made it worse! ...is there a way i can un install them ALL??? and reinstall fresh ones that arent conflicting with eachother or at least get something to work... HELP! I have winxp MCE and MCE doesnt even work now.