You mean white played c4 I suppose (you wrote c5)? Anyway, your pawn would need to be on b4, NOT on b3.
Why cant I take en passant?

For future reference: http://en.wikipedia.org/wiki/En_passant

For further future reference: http://en.wikipedia.org/wiki/Land_snail
Why cant I take en passant here? White played c5 and the game wouldnt let me take. btw the caption is wrong, it is blacks move here. I messed up the diagram.