So, first I would try switching the battery configuration, + for -, if you have them in backwards sometimes only the light will work.
If that isn't the issue, your engine may be "stuck". It seems to me that if there are no wire, connection, or corrosion problems, a lot of these Kenner engines that make the sound effects, just seem to stick in place. This has happened a few times to me with my vintage X wing. The only remedy, and I suggest this with GREAT caution, is to open up your ship and, with the batteries in connection giving power to the light, gently nudge the gear (the one that hits the plastic filament that makes the noise) and it should spring back to life. It may take a couple of tries, with the batteries still connected. Seriously, I have done this several times with my X wing and a couple of TIE fighters, and it does work but the X is really hard to take apart, and the springs on the TIE fighters are a real nuisance to get back in place. PM me with your email addy and I will hit you back with detailed intructions if you want.