Another update -

Before boxing the loco up, I decided to give it another try to make sure I was describing the problem correctly - it behaved erratically - jerking around, odd noises, not sure which way to go, etc. - but I began to wonder if it weren't the power pack (MRC Railpower 1300 from a trainset).  I have an MDC 4-4-0 which had never run, so I took that out of the box and ran it too - it showed a warmup period and then ran reasonably well, but not great either.

I'm wondering if I shouldn't upgrade the power pack.  Can anybody recommend a good DC power pack?

Update -

Thanks to all for your advice - I called Bachmann service and told them about the problem - they said to send the loco back to them and they would have a look at it and let me know.  When they do, if this post hasn't sunk way down, I'll let you know.  Good thing the loco is clearly under warranty.  Gotta say it's a very nice piece of work - looking forward to working it into a New Haven K-1d ...

Luckily, I am not in a huge rush ...

And no, I did not hook up the AC power - I may be new to DCC - but I have been a model railroader (and have read the mags) for over 40 years. 

(Now I guess it's time for me to start reading the manuals!)

Thanks again.

I'm new to owning locos with dual-mode decoders and today I rushed home from the hobby store and put my beautiful new 2-6-0 on my partially-built layout, fired up the cheapi train power 1300 power pack.  Mystified by the flashing lights and jerky operation, and assuming that, as with old fashioned DC locos it just needed more juice, I floored it. All it did then was flash its lights and make pathetic snapping sounds
THEN I consulted the little guide that came with it and realized I probably fried the decoder.
1.  Did I?
2.  If so, how do I get a new decoder and replace it?  Is it easy?

Yes I know I should have read the guide first - won't make THAT mistake again!