Hm ok i thought everything should clear. But i try to describe it more in detail. I hooked up 4 shift registers like so: (example 2) http://arduino.cc/en/Tutorial/ShiftOut.
I am using the shift registers to control 9 rgb less. For this i use the ShiftPWM Library. But this library is only for working with leds, so i cant use this library to get my button value (high or low). I hope its more understandable now ? Sorry but because i dont know how to program this i can't upload a little test sketch.
The clue in in the name shift OUT.
With those shift registers you can only output stuff not input it.
If you want to input information you have to use a different type of shift register.
See the shift in tutorial.