Hi,
There are a few solder joints that would be good to check. The two that stand out are the one by the green wire, and the one by the red wire. Did the solder bridge onto another pad? Are they supposed to be connected? If not, check for continuity between the two joints, and if there is, de-solder the joints, and try again with fresh solder. Also, you might try checking where the voltage comes in to the board (assuming the batteries are good!). Do you get a voltage reading there?
Dave