Hi,
you could make the compilation a bit cleaner if you used something like
g++ -o Output Input.cpp $(root-config --cflags --glibs --ldflags) -lMinuit SomeLibrary.o
Further, are you using Minuit2? In that case you should link against -lMinuit2. Also try using
-Wl,--no-undefined when you link, because it will error out when you have undefined symbols (because you forgot a library when linking).