You could try to return the NXT brick to its factory default and reinstall the firmware, but this won't fix the problem if its something in your code that makes the NXT "look" like its freezing. The reset button for the NXT is on the back of the device at the very bottom of one of its mounting holes near the USB port. If you look down into it you should see what looks like a small silver button. You will need a paper-clip or something similar to press it.
Also if you have another NXT brick its worth testing your code out on it to see if it experiences the same problem. If it does it might be an issue with your code.
-Mark
Mark
NI App Software R&D
