Try getting it up on a 2x4 or some base to see if the tracks move without weight on them. Also make sure your batt is fully charged. Just some basic variables to eliminate before we try and help further. Worse case you may have come across what I did on mine, bum gearboxes out of the box which rc4wd replaced.
https://www.youtube.com/watch?v=8Km26FwRQyM
https://www.youtube.com/watch?v=lVjj6_1bRe0