The Peugeot was doing that - would NOT shift into 1st or 2nd gear no matter what I did, but according to my maintainence book (I bought the Bicycling Mag Bike Maintainence for all types of bikes coz the pictures are Real photos) it was just a matter of adjusting the high/low screws on the back derailleur. If yours is the front, there should be 2 screws on the mount by the front maybe (maybe not) marked H n L. One of them controls the throw down and the other - OK...I'm NOT going to say it....the throw up! (oops...yes I did). I'm guessing that your bike shop guys have played with that, but I guessed my bike shop guys had done the same thing on the Peugeot. All I know is, I played with it myself, and fixed the problem.

Hope this helps.