Want to download something so I can play MPEG4 videos

Help Please - My computer will not play UTubes that have an extension MPEG4. I downloaded RealPlayer with your help and it would convert them to WMV for a few times but then this block came up trying to sell me RealPlayer 16 and it wouldn't go away so I thought they were just giving me a sample and now wanted me to buy the "16" which I did. However, it will still not convert it to WMV, just says "Conversion Failed". I have gone through all the steps to fix this (according to support RealPlayer) but it will still not convert, so am wondering if I could download MPEG4 somewhere safe so I could download some neat videos to my USB plug to watch on TV

Thanks.
Midser:o