Well, working code is the one thing you're not getting from me. This is all from memory (and looking at the docs). I don't have a working ImageMagick install right now, nor the time to get one running.
Anyhow the first code sample looks like what I would try. It's very odd that it is not working! I'm sure it has worked for me in the past.
Anyhow I'd definitely try John's suggestion of the command line tools. Then possibly try converting some other pngs, some jpgs. Just start narrowing down the problem. Something has to work. ImageMagick has been very good to me in the past.
PS. Some 'code' tags would make this much more readable.