Don't chuck the ipod yet, my friend. Remember ebay.
But seriously, I had a very similar problem. The fact that you have a video on your PC doesn't mean that it is playable on itunes which is essential for you to be able to get it on your ipod.
What you must ensure first of all is that the videos and music are playable in itunes instead of what else may be on your computer (e.g. Real Player or Windows Media Player). You will know this because the icons all look like the Itunes icon (a CD with a musical note on it). If it is not in the right format, you may need to convert it (www.youconvertit.com can help). Alternatively, you might need to ensure that itunes is the default player for those items you have downloaded.
Finally, it may help to put the actual items in the itunes folder on your computer. Depending on what's wrong, I suspect your solution lies here somewhere.
Hope this helps.