Hi Elaine, are you sure that they're screws and not nails? Typically it's nails that pop out and the cure is using drywall screws to replace them or secure them in place. The cause is normally attributed to the 2x4's underneath the drywall having been too GREEN when the drywall was put up. As the 2x4's eventually dry out they shrink thereby leaving a larger hole around the nails, which means that the nails no longer are securely attached to the 2x4's. Finally, YES contact the contractor regarding fixing this, 1) it's his responsiblity, 2) it's not difficult, and 3) he/she wants to maintain a good reputation.

Wick