The problem is related to what jalonso and CELS have said already, you need better control of your pixels. This piece has no "form", there's some random light pixels on one side of the face and random dark pixels on the other. To be perfectly blunt it is sloppy. Pixelart is about prescision imho (not in all cases mind you).

Here's a greyscale edit I made showing how it could be less sloppy (I'm bad with colors so excuse the greyscale).

It's not amazing and it's not finished or anything but hopefully it shows you what having more prescision with your pixels can do. I said this before but, tutorials are really helpful..
 

i know where's the forum is... i want to know what is the exsact problem is

http://www.pixeljoint.com/forum/

link plz

I don't think re-submitting them will get these pieces accepted. I believe jalonso suggested going to the WIP forums, I second that. It seems that would be the best place to get help and also tutorials would be helpful.