Tried it several times, and it still doesn't work.  Any other ideas?

We have just purchased a Gandy Dancer for our track and it makes sounds as if it's getting power, but doesn't move.  Does any one know what might be wrong?  Any help would be appreciated.

Like I said, I'm new at this and just thought sounds would be nice.  I know nothing about what diesel locomotives are supposed to sound like, or do they even make a sound?  I'm thinking maybe it's not worth the time and/or money to even worry about it.

Both Locomotives have "DCC Onboard".  Does this mean that I will only need a decoder?  I've seen a little speaker thingie and wasn't sure about what that is is this something that I don't need?

Thank you so much for any info.

I bought a Bachmann FTA and GP40 and am confused as to what exactly I need in order to add sound.  Can someone please give me specifics please.

Thank you.