Difference amplifier show fixed voltage on its output
Hmm so the opamp supply pins are +5 and ground?
The 3.85 V output suggests the opamp is hitting the positive rail.

V(+) should always be 0.5V * 56k/66k. 
Check all the pins and such and make sure you haven't mixed up the inputs.
Then try a new opamp maybe you let the magic smoke out of this one and didn't see it. :^)