Divide and conquer.
Are you sure your part is working?
First off, check your outputs. Hook up the part and put a voltmeter on each axis output. Turn the part over so the axis you are measuring goes in and out of alignment with gravity (ie is aligned up and down) and see if that output acts as expected. Remember, it should be 1g reading to -1g as you turn it over. Then check the other axis.
Check your inputs. Are you trying to do A/D on the chip? Hook up a potentiometer and make sure you input routines work.
It's not rocket science.
Uh oh, maybe it is! Well, at least ballistic missle science!