Screw will not go into interior wall

I am trying to hang up closets organizers for a walk in closet and I could not put a screw into the wall. I tried on 4 spots and it would not go into the wall at all.

I used a magnetic studfinder and i could hardly sense nails.

Here is a picture of the wall after I" removed the cable plug.

http://imageshack.us/photo/my-images/706/photo1idn.jpg/