I have an iPhone 5 and it's absolutely full of videos that I filmed using the camera. Some of these videos though, although they are on my iPhone 5, i actually filmed them back in 2009/2010/2011 using the phone i had at the time which was probably an iPhone 3G (I also had an iPhone 4 at one point). I was just going through my phone to clear stuff off it and stumbled across all these videos...the problem is, the heads of all the people in the videos are cut off!! It's as if the top of the video is cut off. I'm not sure why this is? Can anyone help and is there a resolution to this? It's only on my old videos. I'm guessing it's something to do with the the camera filmed video back in 2010 to the way it does now. A different resolution or something?

Same problem here. You might still have the videos in full, just not viewable correctly on the iPhone. I copied a couple of ones off to another medium and could see them. Have a try.

This is probably a metadata issue and as Amelia says you can almost certainly play them on some other device.
On a similar subject has anyone experience the "upside down" video problem. There is a right way and a wrong way to hold the phone when taking videos - and I mean this seriously, not as in the mocking that is made of Steve Jobs "you're holding it wrong".

The correct way to hold the phone when (in landscape mode for videos) is with the home button on the right hand side. If you do it the other way then videos will look fine when played with any Apple media player but be upside down when displayed in the Windows world. I am left handed and naturally hold it wrong so that is why I am well aware of the problem. At first sight it looks like an Apple problem, but it actually comes down to the fact that Apple support and implement a standard for orientation metadata, whereas Microsoft ignore it.