In post #30 of Robin2's simple rf24 tutorial is a diagnostic sketch to test the hardware connection between the rf24 module and its connected processor. Maybe that will help.
I recommend using an external 3.3V power source for the rf24 modules that is capable of supplying 500mA. That assures enough current. I use home made versions of these adapters.
If you are using the high powered modules (with external antenna), move the modules at least a couple of meters apart. They may not communicate if too close together.