panstamp device signature is random
Is the Panstamp broken ?


Sounds like it. If one works, and the other does not, using the same wiring, it looks like you have a faulty one.


  or should I do a kind of factory reset?


You can't really "factory reset" a chip like that. Possibly there is a problem with the fuses. You may be able to explore further here:

Have I bricked my Arduino Uno? Problems with uploading to board