I need to screw into my wall but halfway in, it hits something hard
Sometimes a concrete wall will not have full-depth studs on it.  Instead it will have thin (sometimes only 3/4") firing strips attached to the concrete and the wallboard or paneling gets attached to those strips.  If you are using long screws, chances are good that you are just hitting the concrete. 

One way to test this would be to drill a small hole where there is not a stud and probe the wall with the bit to see how deep it is.  If the wall is shallow and you have thin firing strips, hanging heavy objects on the wall can be a challenge because you will have to use special anchors and partially drill into the concrete or brick.  You have to know a little more about how the wall is built to know that drilling the concrete will be safe.