Check all the basics like the other guys said: Make sure the battery is charged (could be a faulty charger not doing it's job), battery is properly connected to the ESC, motor wires are properly and fully connected to the ESC (they might have come halfway out, and make sure the positive and negative wires are right), ESC works and is calibrated as per the instructions, radio and receiver are bound (should make a beeping sound or something after both the radio and truck are turned on), there's no excess interference (2.4ghz isn't easily effected, but still), motor, servo, ESC and receiver are good (trouble shoot, instruction manual will help), fresh AAs in the radio, ect.