It's hard to know, but the approach you should use is to simplify to isolate the problem.
Instead of trying to load a complex 3d model first, you could start with a simple plane or cube without a texture, to make sure that the size and position is correct and as you expect. Once confirmed you can add a texture and test again.
Then slowly build up to something more complex.
You need to be able to diagnose where the problem is by slowly trying different things out, and it may help you to show it to a friend or colleague who may be able to help. The other thing you can do is to search the forums, read the FAQ and dev guide, as there are plenty of resources to guide you.
We are here to answer technical queries and will do our best, however the more specific the query and the more details that we have, the more likely we can help.
Hope you can understand.
BTW one thing you can check is that your .png should be square in size and a power of 2 e.g. 256*256