Taking the absolute value of a DC source (getting the magnitude of the voltage)
Please show us your circuit. 
It's very likely some small mistake requiring a quick fix.
The fact it worked in simulation but not on the breadboard makes me suspect it's something like you are not using dual supply rails, or you are not working within the opamps specs (e.g. common mode input range, minimum supply voltage, etc)  

If you show us your circuit it is almost certain this problem will get fixed very quickly, otherwise people will probably give up. Sorry to be blunt but it seems to be a very common issue here, and I feel many questions go unanswered (or are not answered fully) due to communication problems.  

If you don't know how to draw/post a schematic ask and help will be provided. Or even a well taken picture of your circuit (+ power sources) would probably help somewhat.