invisible wall need help plz

I am sorry if this is the wrong place but don’t know where else to ask this I am trying to work on a game the wall is invisible on one side but when i walk to the other side the wall is there but it is the wrong way around how can I make it so I can see the wall? plz help tnx you for your time

http://img844.imageshack.us/img844/2175/invisiblewall.png

Check the normals of the wall in edit mode, (EDIT MODE -> A (select all) -> CTRL + N

a box comes up on the left side saying inside when i hit CTRL + N so do i need to set all the faces. i have select all the faces. can not see normals when i hit CTRL + N i am some what new to blender but not 3d the only thing i have heard a normal is a normalmap but don’t think that is what you mean

oh ok cool i see it now tnx i got to set the faces what are the wrong way around tnx so much